US20090023513A1

US20090023513A1 - Iron golf club

Info

Publication number: US20090023513A1
Application number: US12/100,028
Authority: US
Inventors: Masaki Shibata; Tomoyuki Sakai
Original assignee: Endo Manufacturing Co Ltd
Current assignee: Endo Manufacturing Co Ltd
Priority date: 2007-04-09
Filing date: 2008-04-09
Publication date: 2009-01-22
Also published as: JP5172438B2; JP2008279249A

Abstract

An iron golf club for enhancing the gear effect and accelerating backspin of a ball. The head, which comprises a face part having a ball-hitting surface, a sole part having a ground-contact plane in the bottom portion of the head, a top part, and a hosel part, is configured such that the rigidity on the ground-contact plane side of the bottom portion is lowered by either providing the portion with a cavity or changing its material. Further, the vertical moment of inertia of the head is reduced by disposing a weight in the location of the center of gravity of the head. When the length of the hosel part is 50 mm or longer, the value of the moment of inertia becomes less than 800 g·cm², and when the length of the hosel part is less than 50 mm, the value of the moment of inertia becomes 750 g·cm²or less. These configurations realize a golf club that enhances the gear effect and accelerates spin of a ball.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an iron golf club that enhances the gear effect, and more particularly to an iron golf club that lowers the rigidity of the sole portion of the head, reduces the head moment of inertia, enhances the gear effect, and accelerates ball spin.
2. Description of the Related Art
Various improvements have been made to the golf club over time for enabling stable shots to thereby increase carry and hit the ball to a precise location. In particular, iron-type golf clubs include, for example, a pitching wedge or sand wedge. These iron-type golf clubs, as a rule, are constituted such that the pitch of the face is predetermined, and a sole surface is provided in the lower portion relative to a face surface, which is the ball-hitting surface, and are golf clubs used when ball-hitting accuracy is demanded in particular.
A variety of iron golf club structures have been proposed, and a player selectively uses an iron golf club in accordance with his preferences. Examples include the flat back type, cavity type, pocket cavity type, and hollow construction type. These types of iron golf clubs all commonly have score lines formed in the surface of the face, and feature measures for stabilizing the amount of backspin imparted to the ball. In a shot to place the ball on the green, the hitting stroke is carried out so as to impart backspin (reverse rotation) to the ball and hit the ball high into the air, making it possible to stop the ball at a predetermined location on the target green.
With regard to prior art for increasing the gear effect in order to impart greater backspin to the ball, this applicant has also proposed a golf club of a construction that forms the height-distance, from the horizontal plane on which the surface of the sole of the head makes contact with the ground to the center of gravity of the head, larger than the radius of the ball, making it easier to impart spin to the ball (Refer to Japanese Patent Laid-open Number 2006-149478). Further, this applicant has proposed a golf club of a construction that either increases the flexibility of the face or the relative displacement of the face relative to the head at impact, thereby making it easier to impart spin to the ball (Refer to Japanese Patent Laid-open Number 2007-44445). Furthermore, as an example of improvement technology related to score lines, an iron golf club that forms sharp edges on the score lines to impart backspin to the ball is known (for example, Japanese Patent Laid-open Number 2004-141277).
Generally speaking, a golf club that imparts spin to the ball has score lines formed in the surface of the face as described above. Upon impact, the ball moves relatively along the surface of this face as it spins, and the ball is gripped by the edges of the score lines at this time, imparting stable spin to the ball. To put more spin on the ball, various improvements have been proposed for the surface of the face on which effective score lines are formed.
However, groove profile (marking) rules designed to establish certain restrictions on the formation of this score line groove have been studied internationally, and regulations were recently proposed. That is, as a new regulatory proposal for club face marking and spin generation, first, the value obtained by dividing the gross cross-sectional area of the score line groove by the pitch of the groove (groove width+spacing) will be restricted to 0.0025 square inches per inch (0.0635 mm²/mm). Second, the sharpness of the edge (angle) of a groove will be restricted to a lowest effective radius of 0.010 inches (0.254 mm).
A certain degree of regulation has been applied to score lines for some time, but now stricter regulations are going to be put into place. Therefore, changing the score line groove, for example, carrying out an improvement that makes the angle of the edge of the groove sharper so as to heighten the spin effect will be restricted in the future.
As mentioned above, improvements applied to the score lines of the surface of the face of a golf club will be restricted in the future, and an improvement designed to make the groove edges sharper will be substantially impossible. Therefore, other methods will have to be considered. Enhancing the gear effect to impart more backspin to the ball improves the performance of the golf club, and is not limited to the surface of the face alone. However, even though there are score line regulations that restrict improvements thereto, there is still room for improvement to aspects other than the score line, and this is what is required.

SUMMARY OF THE INVENTION

The present invention has been developed to solve for the problems inherent in the prior art as described hereinabove, and achieves the following object. An object of the present invention is to provide a golf club, which is an iron golf club designed to enhance the gear effect to make it easier to impart spin to a golf ball.
The present invention employs the following means for achieving the above-mentioned object.
An iron golf club of a first invention comprises: a head having, in a lower portion thereof, a sole part which has a ground-contact plane, and having, in an upper portion thereof, a top part, and a face part which has a ball-hitting surface for striking a ball, and, at one end thereof, a hosel part which is a shaft connector; and a shaft, which is connected at one end thereof to the hosel part, a ground-contact plane side of the head being configured to have low rigidity.
An iron golf club of a second invention according to the first invention, the top part side of the head being configured to have relatively higher rigidity than the ground-contact plane side.
An iron golf club of a third invention according to the first invention, the ground-contact plane side of the head having a relatively higher coefficient of rebound than the top part side of the head.
An iron golf club of a fourth invention according to the first through the third inventions, the ground-contact plane side of the head being in an area nearer to the sole part side than to an approximate horizontal plane which is parallel to the score lines, and which passes through the center of gravity.
An iron golf club of a fifth invention comprises: a head having, in a lower portion thereof, a sole part which has a ground-contact plane, and having, in an upper portion thereof, a top part, and a face part which has a ball-hitting surface for striking a ball, and, at one end thereof, a hosel part which is a shaft connector; and a shaft which is connected at one end thereof to the hosel part, and when the length of the above-mentioned hosel part is 50 mm or longer, the value of a moment of inertia centering on the axis that passes horizontally through center of gravity of the above-mentioned head in the toe-heel direction is less than 800 g·cm². Preferably, this moment of inertia can be 770 g·cm²or less.
An iron golf club of a sixth invention comprises: a head having, in a lower portion thereof, a sole part which has a ground-contact plane, and having, in an upper portion thereof, a top part, and a face part which has a ball-hitting surface for striking a ball, and, at one end thereof, a hosel part which is a shaft connector; and a shaft which is connected at one end thereof to the hosel part, and when the length of the above-mentioned hosel part is less than 50 mm, the value of a moment of inertia centering on the axis that passes horizontally through the center of gravity of the above-mentioned head in the toe-heel direction is less than 750 g·cm².
An iron golf club of a seventh invention according to the first through the sixth inventions, the specific gravity of the material that constitutes the main part of the above-mentioned head being 6.5 g·cm²or greater.
An iron golf club of an eighth invention according to the first through the seventh inventions, the above-mentioned head being either the head of a short iron or the head of a wedge.
All of these inventions lower the rigidity of the lower portion of the head and reduce the moment of inertia of the head, thereby increasing the gear effect and making it easier to impart spin. Means such as those described below are effective for achieving this.
Firstly, the head has means for configuring a hollow body having a cavity on the inside of the ground-contact plane side only.
Secondly, the head has means for configuring a hollow body having a cavity on the inside, and for the sole part only to be comprised of a material with a lower Young's modulus than the other parts.
Thirdly, the head has means for configuring a hollow body having a cavity on the inside of the ground-contact plane side only, and for laminating a material with a high mechanical strength composition between the face part and the other parts above this cavity.
Fourthly, the head has means for configuring a hollow body having a cavity on the inside, and for a groove, the wall thickness of which is partially thinner than the other parts, to be formed in the sole part only.
Fifthly, the head has means for configuring a hollow body having a cavity on the inside, and for forming the wall thickness portion of the upper portion of the face part thicker than the wall thickness portion of the lower portion.
Sixthly, the head has means for configuring a hollow body having a cavity on the inside, and for a partially thinner groove to be formed in the lower portion of the face part.
Seventhly, the head has means for configuring a hollow body having a cavity on the inside, and for forming the material composition of the lower portion of the face part at a relatively lower hardness than the material composition of the upper portion in a face part of the same material composition.
Eighthly, the head has means for configuring a hollow body having a cavity on the inside, and for the upper portion and lower portion of the face part to be materials of different composition, and for forming the material of the lower portion into a lower hardness material that is relatively softer than the material of the upper portion.
Ninthly, the head has means for configuring a hollow body having a cavity on the inside, and for the parts other than the face part to be the same material, and for forming the material composition of the lower portion of the head at a relatively lower hardness than the material composition of the upper portion.
Tenthly, the head has means for configuring a hollow body having a cavity on the inside, and for the upper portion and lower portion of the parts other than the face part to be materials of different composition, and for forming the material of the lower portion into a material having a hardness that is relatively softer than the material of the upper portion.
Eleventhly, the head has means for configuring a hollow body having a cavity on the inside, and for the material of the lower portion of the face part to be formed at a relatively lower Young's modulus than the material of the upper portion.
Twelfthly, the head has means for configuring a hollow body having a cavity on the inside, and for the material of the lower portion of the parts other than the face part to be formed at a relatively lower Young's modulus than the material of the upper portion.
Thirteenthly, the head has means for a through-groove, which parallels a score line formed in the ball-hitting surface of the face part, to be formed in the middle portion of the head on the back side of the face part.
Fourteenthly, the head has means for a pocket-shaped groove, which parallels a score line formed in the ball-hitting surface of the face part, and which is open at the tip of the toe side, to be formed in the middle portion of the head on the back side of the face part.
Fifteenthly, the head has means for a groove to be formed perpendicularly to the ground-contact plane in the lower portion of the head up to an intermediate location.
Sixteenthly, the head has means for an elastic member to be disposed in the groove formed perpendicularly to the ground-contact plane in the lower portion of the head up to an intermediate location.
Seventeenthly, the head has means for disposing in the vicinity of the center of gravity of the head a weight for reducing the vertical moment of inertia.
Eighteenthly, the head has means by which the vicinity of the center of gravity of the head, where a weight is disposed to reduce the vertical moment of inertia, is formed in a groove.
Nineteenthly, the head has means for configuring a hollow body having a cavity on the inside, and for a weight for reducing the vertical moment of inertia to be disposed in the vicinity of the center of gravity of the head, and for the above-mentioned cavity to be formed in a vertically intermediate portion of a part other than the face part.
Twentiethly, the head has means for configuring a hollow body having a cavity on the inside, and for a weight for reducing the vertical moment of inertia to be disposed in the vicinity of the center of gravity of the head, and for the above-mentioned cavity to be formed in a vertically intermediate portion of the face part.
Twenty-firstly, the head has means for a weight for reducing the vertical moment of inertia to be disposed in the vicinity of the center of gravity of the head, and for forming a groove in a vertically intermediate portion, and furthermore, for forming a hollow body, which is a cavity, on the inside of the sole part side of the lower portion of this groove.
Twenty-secondly, the head has means for a weight for reducing the vertical moment of inertia to be disposed in the vicinity of the center of gravity of the head, and, in addition, for this weight to be disposed in the upper end of the lower portion of a part of the head other than the face part.
As described in detail hereinabove, the iron golf club of the present invention is such that configuring the head to increase the flexibility of the lower portion of the face, or configuring the head to reduce the moment of inertia, that is, deforming the lower portion of the head to achieve a structure, by which the club readily rotate, makes it possible for the surface of the face to bend backward and rotate in the downward direction, and to lengthen the ball holding (contact) period, thereby enhancing the gear effect more than that of the prior art. Therefore, rotation in the reverse direction is effectively imparted to the ball. Thus, the iron golf club of the present invention is able to impart a greater amount of backspin to the ball.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general view of an iron golf club;

FIG. 2 is a schematic diagram showing the state immediately prior to a ball being impacted by the head;

FIG. 3 is a schematic diagram showing the state immediately after a ball has been impacted by the head;

FIG. 4 is a schematic diagram of an embodiment for reducing rigidity by forming the lower portion of the head as a hollow body;

FIG. 5 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, and giving the material composition of the sole part a lower Young's modulus;

FIG. 6 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the lower portion of the head as a hollow body, and disposing a high strength material in the upper portion;

FIG. 7 is a schematic diagram of an embodiment for reducing rigidity by forming the head as a hollow body, and forming one part of the lower portion of a part other than the face into a groove;

FIG. 8 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, and making the wall thickness of the lower portion of the face thinner than the wall thickness of the upper portion;

FIG. 9 is a schematic diagram of an embodiment for reducing rigidity by forming the head as a hollow body, and forming one part of the lower portion of the face into a groove;

FIG. 10 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, making the face the same material, making the material composition of the upper portion a higher hardness, and making the material composition of the lower portion a lower hardness;

FIG. 11 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, using a high hardness material in the upper portion of the face, and using a low hardness material in the lower portion of the face;

FIG. 12 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, making the parts other than the face the same material, using a high hardness material composition in the upper portion, and using a low hardness material composition in the lower portion;

FIG. 13 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, making the upper portion of a part other than the face a high hardness material, and making the power portion a low hardness material;

FIG. 14 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, making the upper portion of the face a material with a high Young's modulus, and making the lower portion of the face a low Young's modulus material;

FIG. 15 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by forming the head as a hollow body, making the upper portion of a part other than the face a material with a high Young's modulus, and making the lower portion a low Young's modulus material;

FIG. 16 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by providing an approximately horizontal through-groove in the location of the center of gravity on the back surface of the head;

FIG. 17 is a side view of FIG. 16;

FIG. 18 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by providing a pocket groove open on the toe side at the location of the center of gravity on the back surface of the head;

FIG. 19 is a side view of FIG. 18;

FIG. 20 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by providing a slit-shaped groove perpendicularly to the ground-contact plane in the lower portion of the head;

FIG. 21 is a schematic diagram of an embodiment for reducing the rigidity of the lower portion of the head by disposing an elastic body in a slit-shaped groove of the same shape of FIG. 20;

FIG. 22 is a schematic diagram showing the lowering of the vertical moment of inertia of the head;

FIG. 23 is a schematic diagram showing the state of a conventional moment of inertia;

FIG. 24 is a schematic diagram showing the state immediately prior to a ball being impacted by the head using the same type diagram as FIG. 22;

FIG. 25 is a schematic diagram showing the state immediately after a ball has been impacted by the head using the same type diagram as FIG. 22;

FIG. 26 is a schematic diagram of an embodiment for lowering the moment of inertia by providing a weight in a groove in the face side in the vicinity of the center of gravity of the head;

FIG. 27 is a side view of FIG. 26;

FIG. 28 is a schematic diagram of an embodiment for lowering the moment of inertia by forming the head as a hollow body, and disposing a weight in the location of the center of gravity of a part other than the face;

FIG. 29 is a side view of FIG. 28;

FIG. 30 is a schematic diagram of an embodiment for lowering the moment of inertia by forming the head as a hollow body, and disposing a weight in a location in the vicinity of the center of gravity portion of the face;

FIG. 31 is a side view of FIG. 30;

FIG. 32 is a schematic diagram of an embodiment for lowering the moment of inertia by disposing a weight in a location in the vicinity of the center of gravity portion of the back surface of the head;

FIG. 33 is a side view of FIG. 32;

FIG. 34 is a schematic diagram of an embodiment for lowering the moment of inertia by disposing a weight in a location in the vicinity of the center of gravity portion at the end of a part other than the face that rises up from the lower portion of the sole;

FIG. 35 is a side view of FIG. 34;

FIG. 36 is a side view of the head showing the face part in which score lines have been provided; and

FIG. 37 is a schematic diagram of the head showing a through-axis, which is at an angle to an axis that is parallel to the ground-contact plane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be explained below on the basis of the figures. The golf club targeted by the present invention is an iron golf club. FIG. 1 is a general view showing the overall appearance of an iron golf club. FIGS. 2 and 3 are schematic diagrams of side views, with FIG. 2 showing the state immediately prior to a ball being impacted by the head. FIG. 3 shows the state immediately after the ball has been impacted by the head. The basic structure of the iron golf club is widely known, and a detailed explanation will be omitted, but to make it easier to understand the present invention, an outline of the iron golf club will be explained below.
In iron golf club related to the present invention, as shown in FIG. 1, is configured from a head 1, which forms a face part 2 on the front face, a hosel part 3, which is the shaft connector to the shaft side, a top part 4 in the upper portion, a toe part 5 in the front portion, and a sole part 6 in the lower portion, which makes contact with the ground; and a shaft 7, which is connected to the hosel part 3 of this head 1. Further, the angle of tilt of the ball-hitting surface relative to a perpendicular line (vertical line) to the ground-contact horizontal plane 11 of the sole part 6 is the loft angle δ (Refer to FIG. 2).
Score lines 8 are carved into the ball-hitting surface of the face part 2. The invention of the golf club, in which the height from the ground-contact horizontal plane 11 of the sole part 6 up to the location of the head's center of gravity 9 is formed to be larger than the radius of the ball 10, is the proposal of the same applicants as those of the present invention, but since the present invention offers an effective structure for the spin effect, this golf club will be used as an example for explaining the spin effect. As shown in FIGS. 2 and 3, on the downswing, the head 1 describes a circular arc relative to the ball 10 so as to get under the ball 10 at impact.
At this time, the ball-hitting surface of the face part 2 makes contact and hits the ball 10 by getting under the ball 10. The result is that the ball 10 indents slightly at impact, catches on the edges of the score lines 8, rotates in a counterclockwise direction as indicated by Arrow A of FIG. 3, and backspin is imparted to the ball 10. In accordance with the swing at impact, the ball 10 moves upwardly in relation to the ball-hitting surface in the direction indicated by Arrow B in the figure, and, while spinning, is hit in the direction indicated by Arrow C.
When the ball 10 is impacted by the head 1 upon being hit, since the height D of the center of gravity 9 of the head 1 is above the center of the ball 10, the sole part 6 side of the ball-hitting surface is momentarily pulled down, and the ball-hitting surface moves rotationally in the clockwise direction as if to rise up. That is, the loft angle δ momentarily becomes smaller (refer to FIG. 3), and as a result, generates a gear effect which imparts spin to the ball 10 in the opposite direction of the rotational movement of this ball-hitting surface, accelerating the backspin. Further, the applicant of the present invention has also proposed enhancing the spin effect via another method, but the figures do not show the other invention (Refer to Japanese Patent Laid-open Number 2007-44445).
This is the result of providing a displacement part, by which either the flexibility of the face, or the relative displacement of the face relative to the head increases at impact. More specifically, continuous peripheral grooves are provided on both sides of the face, and displacement grooves are provided on the front side of the face in only three directions: toward the top side edge, the toe side edge and the leading edge. Upon impact, these displacement grooves generate relative displacement, which has the heel side as the center of rotation and becomes larger at the toe side, making it easy to hit the ball using the gear effect.
These technologies are effective in their own ways, but as mentioned above, improvements to the ball-hitting surface of the face part 2, such as changing the performance of the score lines 8 in particular, are restricted by new regulations. Therefore, an optimum method must be devised by improving a part other than the surface of the face part 2. With regard to the face part 2, the ball 10 is normally impacted by the lower portion of the face. As described hereinabove, the impacted ball 10 moves up the score-lined ball-hitting surface while relatively making contact with the score lines 8, and the ball 10 rotates in the counterclockwise direction, being imparted with backspin.
In support of this, the present invention has been configured such that, when the ball 10 is impacted by the lower portion of the face, the structure of the lower portion of the head changes so as to make the backward bending of this lower portion vary relatively easily. That is, as described hereinabove, in this embodiment for enhancing the gear effect, the ball-hitting region of the lower portion of the face in particular moves relatively rotationally toward the rear at impact having the location of the center of gravity 9 of the head 1 as the fulcrum, that is, the head 1 is structured so as to be able to bend backward.
By so doing, the ball 10 does not immediately move subsequent to impact, but rather, the lower portion of the face moves relatively rotationally backward, that is, the lower portion of the face readily bends backward, thereby allowing the ball 10 to held at (be in contact with) the ball-hitting surface longer. As a result, the movement of the ball 10 up the ball-hitting surface is lengthened, that is, the contact time increases, thereby promoting the grip on the ball 10 and increasing the gear effect, resulting in the ball 10 being hit with a lot of backspin. Thus, the present invention is constituted to solve for the problems described above, and to further increase the gear effect and accelerate spin. This embodiment will be explained more specifically below.

Embodiments for Reducing Rigidity of Lower Portion of Head

This embodiment is an example of a constitution that reduces the rigidity of the lower portion of the head, that is, a constitution that uses a flexible structure or a readily deformable structure, and imparts a relative rotational movement to the head at impact, thereby enhancing the gear effect and accelerating the backspin of the ball.
The iron head shown in FIG. 4 has a hollow body having a cavity 20 on the inside only in the lower portion of the head 1, that is, on the ground-contact plane side of the sole part. This cavity 20 is a void of the ground-contact plane side surrounded by the back side of the face part 21 and a part 22 other than the face part 21. This is an example in which the lower portion is given lower rigidity and made flexible by making the upper portion solid and forming a cavity in the lower portion so as to relatively vary vertical rigidity. Furthermore, the rigidity referred to in the present invention is defined as follows. When a load P acts on one part of a solid, and the amount of deformation generated at this load point is represented as u, the amount of deformation u in an elastic body is proportional to the load P. That is, the equation becomes u=αP. This proportional constant α is flexibility, and rigidity is represented by 1/α=K.
The iron head shown in FIG. 5 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the material composition of the lower portion of the head 1, that is, the material composition of the sole part side of a part 24 other than the face part 21 of the ground-contact plane, uses a material with a low Young's modulus 25. This is another example in which the ground-contact plane side is made flexible by making the rigidity lower than that of the upper portion.
The iron head shown in FIG. 6 is an example in which the lower portion of the head 1, that is, the ground-contact plane side only is configured into a hollow body having a cavity 20 on the inside, and a high strength material 27 is disposed so as to be sandwiched between the face part 21 of the upper portion of the head 1 and a part 26 other than the face part 21. This is another example of making the ground-contact plane side flexible by making the rigidity lower than that of the upper portion so as to relatively vary the rigidity of the lower portion and upper portion of the head 1.
The iron head shown in FIG. 7 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and inside this cavity 23 a groove 29 is provided in the lower portion of the head in one portion of the ground-contact plane side of a part 28 other than the face part 21. This example is one that makes the ground-contact plane side of the head 1 flexible by using a groove 29 to make the rigidity lower than that of the upper portion.
The iron head shown in FIG. 8 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and a step is provided in the wall thickness of the face part 30. That is, the configuration of the face 30 is constituted such that the ball-hitting surface of the face part 30 is flush, and a step is provided inside the cavity 23 thereof, thereby making the upper portion thick-walled 31 and the lower portion thin-walled 32. As a result, the rigidity of the lower portion of the face part 30 is made lower than that of the upper portion, thereby making the lower portion of the head flexible.
The iron head shown in FIG. 9 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and a groove 34 is provided in the lower portion of the face part 33. That is, the face configuration is such that the ball-hitting surface of the face part 33 is flush, and a groove 34 is provided on the backside of the face part 33 in one portion of the ground-contact plane side. Consequently, this example is one in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the face part 33 lower than that of the upper portion.
The iron head shown in FIG. 10 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the hardness of the upper portion and lower portion of the face part 35 differs. That is, the face part 35 comprises the same material, but the upper portion comprises a high hardness composition 35 a, and the lower portion comprises a low hardness composition 35 b. The constitution is such that the rigidity of the upper portion and lower portion of the face part 35 varies relatively in accordance with the difference in material hardness between the high hardness composition 35 a and the low hardness composition 35 b. As a result, this is an example in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the face part 35 lower than that of the upper portion.
The iron head shown in FIG. 11 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the hardness of the material used in the upper portion and lower portion of the face part 36 differs. That is, it is a configuration in which the upper portion of the face part 36 comprises a high hardness material 36 a, and the lower portion comprises a low hardness material 36 b, and the different hardness materials are welded together. The constitution is such that the rigidity of the upper portion and lower portion of the face part 36 varies relatively in accordance with the difference in hardness between the high hardness material 36 a and the low hardness material 36 b. As a result, this is an example in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the face part 36 lower than that of the upper portion.
The iron head shown in FIG. 12 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the hardness of the upper portion and lower portion of a part 37 other than the face part 21 differs. That is, the part 37 other than the face part 21 comprises the same material, but the upper portion comprises a high hardness composition 37 a, and the lower portion comprises a low hardness composition 37 b. The constitution is such that the rigidity of the upper portion and lower portion of the part 37 other than the face part 21 varies relatively in accordance with the difference in hardness between the high hardness composition 37 a and the low hardness composition 37 b. As a result, this is an example in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the part 37 other than the face part 21 lower than that of the upper portion.
The iron head shown in FIG. 13 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the hardness of the upper portion and lower portion of a part 38 other than the face part 21 differs. That is, it is a configuration in which the upper portion of the part 38 other than the face part 21 comprises a high hardness material 38 a and the lower portion comprises a low hardness material 38 b, and the two different hardness materials are welded together. The constitution is such that the rigidity of the upper portion and lower portion of the part 38 other than the face part 21 varies relatively in accordance with the difference in hardness between the high hardness material 38 a and the low hardness material 38 b. As a result, this is an example in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the part 38 other than the face part 21 lower than that of the upper portion.
The iron head shown in FIG. 14 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the upper portion and lower portion of the face 39 comprise a different Young's modulus. That is, it is a structure in which the upper portion of the face part 39 comprises a material with a high Young's modulus 39 a, the lower portion comprises a material with a low Young's modulus 39 b, and the two different Young's modulus materials are welded together. The constitution is such that the rigidity of the upper portion and lower portion of the face part 39 varies relatively in accordance with the difference in the Young's modulus between the high Young's modulus material 39 a and the low Young's modulus material 39 b. As a result, this is an example in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the face part 39 lower than that of the upper portion.
The iron head shown in FIG. 15 is an example in which the head 1 is configured as a hollow body having a cavity 23 on the inside, and the Young's modulus of the upper portion and lower portion of a part 40 other than the face part 21 differs. That is, it is a configuration in which the upper portion of the part 40 other than the face part 21 comprises a high Young's modulus material 40 a, the lower portion comprises a low Young's modulus material 40 b, and the two different Young's modulus materials are welded together. The constitution is such that the rigidity of the upper portion and lower portion of the part 40 other than the face part 21 varies relatively in accordance with the difference in the Young's modulus between the high Young's modulus material 40 a and the low Young's modulus material 40 b. As a result, this is an example in which the lower portion of the head is made flexible by making the rigidity of the lower portion of the part 40 other than the face part 21 lower than that of the upper portion.
Furthermore, a method other than those cited above, such as heat treatment, can be selected as means for varying the hardness or Young's modulus.
The iron head shown in FIG. 16 is an example in which a through-groove 42, which is provided on the back side of the head 41, and which parallels the score lines formed in the ball-hitting surface of the face part, is formed in the intermediate portion of the head on the back side of the face part. FIG. 17 is a side view of FIG. 16. The through-groove 42 is a groove that passes through (penetrates) the head 41 from the toe part 5 side to the hosel part 3 side. Since the intermediate portion of the head 41, which is configured by the through-groove 42, constitutes a lower rigidity than that of the upper portion and lower portion of the head 41, the configuration is such that the lower portion of the head 41 is flexible at impact. Consequently, the lower portion of the head 41 has lower rigidity and is flexible.
The iron head shown in FIG. 18 is an example in which a pocket-shaped groove 44, which is provided on the back side of the head 43, parallels the score lines formed in the ball-hitting surface of the face part, and is open at the tip of the toe side, is formed in the intermediate portion of the head 43 on the back side of the face part. FIG. 19 is a side view of FIG. 18. The tip of the toe part 5 side of the pocket-shaped groove 44 of this iron head is open, and since this pocket-shaped groove 44 part has low rigidity, the lower portion of the head 43 is flexible at impact. Consequently, the lower portion of the head 43 has lower rigidity and is flexible.
The iron head shown in FIG. 20 is an example of a configuration in which a groove 46 is formed in the lower portion of the head 45 approximately perpendicularly (vertically) from the ground-contact plane, more accurately, at a sharp angle (practically the loft angle) from the vertical, up to an intermediate location. It is an example in which the groove 46 is provided in a slit shape in a part 47 other than the face part, which is practically integrated with the back side of the face part, and the wall thickness of the lower portion of the face part is relatively thinner than the wall thickness of the upper portion of the face part. In accordance with this configuration, the lower portion of the head becomes flexible at impact. Consequently, the lower portion of the head has lower rigidity and is flexible.
The iron head shown in FIG. 21, like that of FIG. 20, is an example in which a groove 46 is formed from the bottom surface of the sole part up to an intermediate location in the direction of the ground-contact plane loft angle relative to the lower portion of the head 45, and an elastic member 48, such as a piece of rubber or a piece of plastic, is disposed in this groove 46. This is another example in which the lower portion of the head is configured to be flexible at impact, and consequently, the lower portion of the head has lower rigidity and is thereby flexible.

Embodiments for Reducing the Moment of Inertia

These are examples in which the configurations are designed to reduce the vertical moment of inertia of the head to facilitate the bending of the head at impact, thereby imparting relative rotational movement to the head upon impact, enhancing the gear effect and accelerating the backspin of the ball.
The iron head shown in FIG. 22 is a schematic diagram showing an example of a head that reduces the vertical moment of inertia. FIG. 23 shows the head of an iron golf club in the configuration of the prior art as a comparative example. The center of gravity of the head is in the same location in the examples of both FIG. 22 and FIG. 23. The differences between these two examples will be explained. In the case of the prior art iron head shown in FIG. 23, there is significant resistance to the relative rotational movement of the head 51. This shows a state in which the head 51 resists rotation, and the vertical moment of inertia around the location of the center of gravity of this head 51 exceeds 850 g·cm².
By contrast, in the case of the iron head shown in FIG. 22, the inventor reduced the resistance of the head 50 to relative rotational movement, and made it easier for the head to rotate by changing the configuration of the head 50 rather than changing the surface of the face of the head 50. The difference in the size of the moment of inertia with the iron head shown in FIG. 23 is illustrated by the rotating arrows a and b. The iron head shown in FIG. 24 illustrates the state immediately prior to the ball 53 being impacted by the face part 52 of the head 50, and when the ball 53 is impacted by the head 50, this state changes as shown in FIG. 25. Spin is imparted to the ball 53, and the ball 53 rotates in the counterclockwise direction as illustrated by arrows, moving relatively along the ball-hitting surface of the face 52.
Further, the position of the head 50 immediately prior to impact changes from that illustrated by the dotted lines 50 a to the position illustrated by the solid lines shown in the figure. This state generates a vertical moment of inertia relative to the head 50, and the head 50 moves relatively rotationally around the location of the center of gravity 54. The moment of inertia of the head 50 becomes small, and the rotational deformation becomes larger than that shown in FIG. 23. As a result, in the case of the iron head shown in FIG. 22, the vertical moment of inertia is less than 800 g·cm²when the hosel part is 50 mm or longer (This definition will be explained hereinbelow.).
As described hereinabove, an iron golf club constituting the present invention is configured from a head 1, comprising: a sole part 6 having, in the lower portion thereof, a ground-contact plane, and having, in the upper portion thereof, a top part 4, and a face part 2 having a ball-hitting surface for striking a ball, and at one end thereof a hosel part 3 which is a shaft connector; and a shaft 7, which is connected at one end thereof to the hosel part 3. When the length of this hosel part 3 is 50 mm or longer, the value of the moment of inertia around an axis that passes horizontally in the toe-heel direction through the center of gravity of the head 50 is less than 800 g·cm².
Further, when the length of this hosel part 3 is less than 50 mm, the value of the moment of inertia around an axis that passes horizontally in the toe-heel direction through the center of gravity of the head 50 is less than 750 g·cm². A specific embodiment of this will be explained next. To reduce the moment of inertia, a weight will be disposed in the vicinity of the location of the center of gravity of the head.
The iron head shown in FIG. 26 is a configuration in which a weight 55 for reducing the vertical moment of inertia is disposed in the vicinity of the center of gravity of the head 56, a groove 57 is formed in the face side of the vicinity of the center of gravity thereof, and the weight 55 is disposed in this groove 57. FIG. 27 is a side view of FIG. 26. The weight 55 is disposed in a location that is centered around an axis that passes horizontally through the location of the center of gravity of the head 56 in the toe-heel direction approximately parallelly to the ground-contact plane, that is, from the tip portion of the toe part 58 side to the hosel part 59 side.
Further, the sole part side portion 60 of the head 56 is configured as a hollow body 62 having a cavity 61 on the inside. Furthermore, although not shown in the figure, the upper portion of this hollow body 62 can be opened to form an indentation. Using this configuration decreases the weight of the lower portion of the head, thereby reducing the moment of inertia and at the same time lowering the rigidity of the lower portion of the head.
The iron head shown in FIG. 28 is an example in which the head 64 is configured as a hollow body having a cavity 65 on the inside, and a weight 63 for reducing the vertical moment of inertia is disposed in the vicinity of the center of gravity of the head 64. FIG. 29 is a side view of FIG. 28. The weight 63 is disposed in a location in the vicinity of the center of gravity of a part 66 other than the face part. The weight 63 is disposed in the intermediate portion of a location that is centered around an axis that passes horizontally in the toe-heel direction through a location in the vicinity of the center of gravity of the head 64, and approximately parallelly to the ground-contact plane, that is, from the toe part 58 side to the hosel part 59 side.
The iron head shown in FIG. 30 is an example in which the head 68 is configured as a hollow body having a cavity 65 on the inside, and a weight 67 for reducing the vertical moment of inertia is disposed in the vicinity of the center of gravity of the head 68. FIG. 31 is a side view of FIG. 30. The weight 67 is disposed in the intermediate portion of a location that is centered around an axis that passes horizontally in the toe-heel direction through a location in the vicinity of the center of gravity of the head 68, and approximately parallelly to the ground-contact plane, that is, from the toe part 58 side to the hosel part 59 side.
The iron head shown in FIG. 32 is an example in which a weight 70 is disposed in the vicinity of the center of gravity on the back side of the head 71. FIG. 33 is a side view of FIG. 32. This example is a configuration, which is similar to opening the upper portion of the hollow body 62 of the iron head shown in FIG. 26 to form an indentation. The weight 70 is disposed along a location in the vicinity of the center of gravity of the head 71, and approximately parallelly to the ground-contact plane the same as in the iron head shown in FIG. 26. That is, the weight 70 is disposed in a location centered on an axis that passes horizontally in the toe-heel direction from the tip of the toe part 58 side to the hosel part 59 side.
The iron head shown in FIG. 34 is an example in which a weight 72 for reducing the vertical moment of inertia is disposed in a location in the vicinity of the center of gravity of the head 73, near the top of a part 74 other than the face part that rises upward from the lower portion of the head, that is, near the tip of the upper portion (apex) 74 a, and in a location in the vicinity of the center of gravity. FIG. 35 is a side view of FIG. 34. The weight 72 is dispose in the intermediate portion between the top and the sole, and is centered on an axis passing horizontally in the toe-heel direction through a location in the vicinity of the center of gravity of the head 73, and approximately parallelly to the ground-contact plane, that is, from the toe part 58 side to the hosel part 59 side.
The iron head shown in FIG. 36 is a side view showing the score lines 8 in the face part 2. The score lines 8 of the iron head 1 shown in FIG. 36 are placed above the ground-contact plane 11 so as to be parallel in relationship to the ground-contact plane 11 of the sole part 6. In this example, location G is a location approximately ½ the height (vertically) from the top part 4 of the face part 2 plane to the sole part 6. This location G is accurately projected perpendicularly to the face plane of the face part 2 from the center of gravity of the head 1.
A horizontal axis P, which passes through this location G, is parallel to the score lines 8, and, in addition, is approximately parallel to the ground-contact plane 11. A horizontal plane comprising this horizontal axis P constitutes the approximate horizontal axis P for the ball-hitting surface of the face part 2. The head 1 of this embodiment is constituted so as to lower the rigidity and enhance the coefficient of rebound of the portion below the approximate horizontal plane passing through this location G, that is, the sole part of the ground-contact plane 11 side.
Further, it is possible to reduce the moment of inertia by making the region near this location G heavier than the other member. The hosel part 3 is generally vertically closer to the top part 4 side than to this location G. Thus, when the length (L) of the hosel part 3 is long, the center of gravity of the head 1 moves relatively closer to the top part 4 side. Therefore, when the length (L) of the hosel part 3 is short, the center of gravity of the head 1 moves relatively closer to the sole part 6 side, thereby consequently contributing toward lowering the location of the center of gravity, and reducing the moment of inertia. Furthermore, it is supposed that length (L) of the hosel part is the length the center line of the hosel part from the point where this line intersects the upper end plane of the hosel part to the point where it intersects the sole plane (refer to FIG. 37).
The iron head shown in FIG. 37 shows an example of a shape in which an axis passing through location G is higher (has greater taper) at the toe side of the top part 4 than at the heel side, as shown in FIGS. 27, 29, 31, 33 and 35. That is, as shown in FIG. 36, the head 1 is positioned so that the score lines become horizontal. At this time, the angle formed by an axis that runs parallel to the upper surface of the top part 4 toward the hosel part 3 and the ground-contact plane 11 is the angle of intersection α. A line segment that passes through approximately ½ the angle of this angle of intersection α is treated as a through-axis S. The relationship between the axis line S of this through-axis and the central axis line of the shaft 7 is closer to that of a right angle than the relationship between the axis line S of the through-axis and an axis line parallel to the ground-contact plane 11. The examples of the respective heads shown in the above-mentioned FIGS. 27, 29, 31, 33, and 35 constitute configurations that dispose weights along an axis close to this through axis S.
It is preferable that the specific gravity of the material for configuring the main parts of the head for reducing the vertical moment of inertia described hereinabove is 6.5 g·cm³or greater. Further, it is preferable that the target iron golf club has a large loft angle, and be used as either a so-called short iron or a wedge. The embodiments of the present invention are configured as described hereinabove, but, needless to say, the present invention is not limited to these embodiments.

Embodiment 1

Next, tests were carried out to show the effect of an embodiment of the present invention. The golf club head used in the tests was related to the iron head shown in FIGS. 32 and 33, and the results of the test hits using the first through the third embodiments are shown in Table 1. In this example, the length (L) of the hosel part was 54 mm, and an iron head, which, with the exception of the sole part, did not have a built-up thickness on the back side, that is, had a plate-shaped face, was used. The configuration was such that the weight 70 of FIG. 32 was affixed as surplus thickness to this plate-shaped face at the location of the center of gravity, and this weight weighed 100 g. The first through the third embodiments changed the moment of inertia by gradually changing the location of this weight. The respective moments of inertia ranged from 715 g·cm²to 770 g·cm². The score lines were formed using a press.
In the comparative example, the moment of inertia using the same method was 800 g·cm². Prior art 1 is a normal muscle back wedge, and the score lines were formed using a press. Prior art 2 forms the score lines using engraving (cutting with a tool). Engraving produces a sharper score line angle than press forming, and in the past this method was used to increase the amount of spin, but this will be regulated in the future as mentioned hereinabove. The hitting tests were carried out at a head speed of 30 m/s, and used the same conditions for prior art and comparative examples. The results of these test hits showed the effect of the example of this proposal shown in FIG. 22 as compared to the prior art shown in FIG. 23.
TABLE 1

Measured Values for Moments of Inertia

(Example Using Prior Art of FIG. 32)

Compara- Embodi- Embodi- Embodi-

Prior Prior tive ment ment ment

Art 1 Art 2 Example 1 2 3

Hosel 73 73 54 54 54 54

Length

(mm)

Moment 980 980 800 770 740 715

of

Inertia

(g · cm²)

Amount 9045 9430 8965 9185 9200 9358

of Spin

(rpm)

When the moment of inertia was 800 g·cm², the amount of spin was almost identical to the amount of spin in Prior Art 1, and when the value of the moment of inertia became smaller, the amount of spin increased. From these, it has been proved that when the hosel length is 50 mm or more, the moment of inertia can be 800 g·cm²or less. From these results, when the hosel length is 50 mm or less, the moment of inertia can be less than 750 g·cm².

Embodiment 2

This is an embodiment of golf clubs related to the iron heads shown in FIGS. 20 and 21, and the results of test hits at X through W of the face part shown in FIG. 36 are shown in Table 2. In this example, the thickness of the face at the slit part was 2 mm, the slit width was 1.5 mm, and the depth of the slit from the bottom surface of the sole was 30 mm. The test-hit locations are at right angles to the score lines as shown in the figure, and treating the location of the center of gravity G as the boundary, prescribe the top part side locations as X and Y, and the sole part side locations as Z and W.
The respective test-hit locations are at the same locations in the toe-heel direction, and are positioned 5 mm apart between the top part and the sole part. As a result, the data in Table 2 below demonstrates that the coefficient of rebound figures at the location of the center of gravity boundary and on the sole part side of this boundary were higher than those of the prior art, which did not have a slit.

TABLE 2

Measured Coefficient of Rebound Values

Location	Prior Art	Example of FIG. 20

X	0.670	0.667
Y	0.752	0.750
G	0.769	0.770
Z	0.750	0.757
W	0.670	0.682

Further, the figures for the amount of spin were larger than those of the prior art as shown in Table 3. The head speed for these test hits was 30 m/s.

TABLE 3

Measured Spin Values

	Prior Art	Example of FIG. 20

	Ball Rotation Speed (rpm)	9045	9528

Claims

1. An iron golf club, comprising:

a head having, in a lower portion thereof, a sole part which has a ground-contact plane, and having, in an upper portion thereof, a top part, and a face part which has a ball-hitting surface for striking a ball, and, at one end thereof, a hosel part which is a shaft connector; and

a shaft, which is connected at one end thereof to the hosel part,

a ground-contact plane side of the head being configured to have low rigidity.

2. The iron golf club according to claim 1, wherein a top part side of the head is configured to have relatively higher rigidity than the ground-contact plane side.

3. The iron golf club according to claim 1, wherein the ground-contact plane side of the head has a relatively higher coefficient of rebound than the top part side of the head.

4. The iron golf club according to claim 1, wherein the ground-contact plane side of the head is in an area nearer to the sole part side than to an approximate horizontal plane which is parallel to a score line, and which passes through a location of the center of gravity.

5. An iron golf club, comprising:

a shaft, which is connected at one end thereof to the hosel part, wherein

when a length of the hosel part is 50 mm or longer, a value of a moment of inertia centering on an axis that passes horizontally in a toe-heel direction through the center of gravity of the head is less than 800 g·cm².

6. An iron golf club, comprising:

a shaft, which is connected at one end thereof to the hosel part, wherein

when a length of the hosel part is less than 50 mm, a value of a moment of inertia centering on an axis that passes horizontally in a toe-heel direction through the center of gravity of the head is less than 750 g·cm².

7. The iron golf club according to claim 1, wherein a specific gravity of a material for configuring the main parts of the head is 6.5 g·cm²or greater.

8. The iron golf club according to claim 1, wherein the head is either the head of a short iron or the head of a wedge.

9. The iron golf club according to claim 2, wherein the ground-contact plane side of the head is in an area nearer to the sole part side than to an approximate horizontal plane which is parallel to a score line, and which passes through a location of the center of gravity.

10. The iron golf club according to claim 3, wherein the ground-contact plane side of the head is in an area nearer to the sole part side than to an approximate horizontal plane which is parallel to a score line, and which passes through a location of the center of gravity.

11. The iron golf club according to claim 6, wherein a specific gravity of a material for configuring the main parts of the head is 6.5 g·cm²or greater.

12. The iron golf club according to claim 6, wherein the head is either the head of a short iron or the head of a wedge.