IRON GOLF CLUB SET

The present application claims priority on Patent Application No. 2010-278723 filed in JAPAN on Dec. 15, 2010, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an iron golf club set having a plurality of iron type golf clubs.

2. Description of the Related Art

An iron golf club set having a plurality of iron type golf clubs is commercially available. Usually, the club set includes a plurality of clubs having different real loft angles, lie angles, and lengths. Each of the clubs constituting the set is distinguished by an iron number. Specification of a head is determined for every iron number based on various respects.

Japanese Utility Model Application Publication (JP-Y) No. 7-49970 discloses an iron golf club set. In the iron golf club set, a sole width on a long iron club side with a 5-iron or a 6-iron as a boundary is formed to be sequentially greater as an iron number becomes smaller, and a sole width on a short iron side is formed to be sequentially greater as an iron number becomes greater.

SUMMARY OF THE INVENTION

The present inventor considered optimization of a sole width in an iron set from a respect different from that of the conventional technique. As a result, the present inventor attained specification of the sole width capable of exhibiting an effect different from that of the conventional technique.

It is an object of the present invention to provide a golf club set capable of appropriately exhibiting a function required for each of iron numbers.

A club set according to the present invention includes n iron golf clubs (n is an integer equal to or greater than 2). Toe side sole widths d1 of the clubs are defined as d1(1), d1(2), . . . , d1(n) in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. A maximum value of the toe side sole widths d1 is defined as d1max. A minimum value of the toe side sole widths d1 is defined as d1min. Heel side sole widths d2 of the clubs are defined as d2(1), d2(2), . . . , d2(n) in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. A maximum value of the heel side sole widths d2 is defined as d2max. A minimum value of the heel side sole widths d2 is defined as d2min. Bounce angles θ1 of the clubs are defined as θ1(1), θ1(2), . . . , θ1(n) in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. A maximum value of the bounce angles θ1 is defined as θ1max. A minimum value of the bounce angles θ1 is defined as θ1min. At this time, the club set satisfies θ1(1)≦θ1(2)≦ . . . θ1(n). The maximum value d1max is substantially equal to the minimum value d1min. The maximum value d2max is substantially equal to the minimum value d2min.

Preferably, a difference (d1max−d1min) is equal to or less than 1.0 mm. Preferably, a difference (d2max−d2min) is equal to or less than 1.0 mm.

In a preferred aspect, the club set satisfies d1(1)≦d1(2)≦ . . . ≦d1(n), and d2(1)≦d2(2)≦ . . . d2(n).

In another preferred aspect, the club set satisfies d1(1)≧d1(2)≧ . . . ≧d1(n), and d2(1)≧d2(2)≧ . . . ≧d2(n).

Preferably, the difference (d1max−d1min) is equal to or less than 0.8 mm. Preferably, the difference (d2max−d2min) is equal to or less than 0.8 mm.

The iron golf club set can appropriately exhibit the function required for each of the iron numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a golf club set according to one embodiment of the present invention;

FIG. 2 shows a perspective view of a head used in the set of FIG. 1;

FIG. 3 shows a front view and bottom view of the head of FIG. 2;

FIG. 4 shows a cross sectional view taken along line F4-F4 of FIG. 3;

FIG. 5 shows a cross sectional view taken along line F5-F5 of FIG. 3; and

FIG. 6 shows a cross sectional view taken along line F6-F6 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate references to the drawings.

A golf club set 2 shown in FIG. 1 is an iron golf club set. A real loft angle L1 of the iron type golf club is usually 15 degrees or greater and 70 degrees or less.

The club set 2 includes a plurality of iron type golf clubs 4 having different real loft angles L1. The golf club set 2 has eight golf clubs 4. The number of the clubs of the golf club set 2 is equal to or greater than 2. In respect of emphasizing an effect of the present invention, the number n of the clubs is preferably equal to or greater than 3, more preferably equal to or greater than 5, and particularly preferably equal to or greater than 6. In the golf rule, the number of the clubs capable of being used during play is restricted. In this respect, the number n of the clubs is preferably equal to or less than 12, more preferably equal to or less than 11, and still more preferably equal to or less than 10.

Each of the golf clubs 4 has a shaft sf, a head hd, and a grip gp. The head hd is mounted to a tip part of the shaft sf. The grip gp is mounted to a back end part of the shaft sf.

The eight golf clubs 4 are a first golf club c1, a second golf club c2, a third golf club c3, a fourth golf club c4, a fifth golf club c5, a sixth golf club c6, a seventh golf club c7, and an eighth golf club c8 in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. The lower an iron number is, the smaller the real loft angle L1 of the head hd is.

The first golf club c1 has a shaft sf1, a head hd1, and a grip gp. The second golf club c2 has a shaft sf2, a head hd2, and a grip gp. The third golf club c3 has a shaft sf3, a head hd3, and a grip gp. The fourth golf club c4 has a shaft sf4, a head hd4, and a grip gp. The fifth golf club c5 has a shaft sf5, a head hd5, and a grip gp. The sixth golf club c6 has a shaft sf6, a head hd6, and a grip gp. The seventh golf club c7 has a shaft sf7, a head hd7, and a grip gp. The eighth golf club c8 has a shaft sf8, a head hd8, and a grip gp.

The golf clubs 4 constituting the golf club set 2 have different club lengths. The golf clubs 4 are the first golf club c1, the second golf club c2, the third golf club c3, the fourth golf club c4, the fifth golf club c5, the sixth golf club c6, the seventh golf club c7, and the eighth golf club c8 in an order from the club having the longest club length. The lower the iron number is, the longer the club length is. The club length is mainly adjusted by the length of the shaft sf. The golf clubs 4 having the same length may be included.

Although not shown in the drawings, the golf clubs 4 constituting the golf club set 2 have different lie angles. The golf clubs 4 are the first golf club c1, the second golf club c2, the third golf club c3, the fourth golf club c4, the fifth golf club c5, the sixth golf club c6, the seventh golf club c7, and the eighth golf club c8 in an ascending order of a lie angle from the club having the smallest lie angle. The lower the iron number is, the smaller the lie angle is. The golf clubs 4 having the same lie angle may be included.

In the embodiment of FIG. 1, the first golf club c1 is a 4-iron. The second golf club c2 is a 5-iron. The third golf club c3 is a 6-iron. The fourth golf club c4 is a 7-iron. The fifth golf club c5 is an 8-iron. The sixth golf club c6 is a 9-iron. The seventh golf club c7 is a pitching wedge (PW). The eighth golf club c8 is an approach wedge (AW). In the present invention, the iron numbers of the golf clubs 4 included in the golf club set 2 are not restricted.

FIG. 2 shows a perspective view of the head hd2 of the golf club c2 (5-iron). FIG. 3 shows a front view and bottom view of the head hd2. In FIG. 3, the front view is drawn on the upper side, and the bottom view is drawn on the lower side. Hereinafter, the head hd2 is described as an example. Structures of heads having the other iron numbers are the same as that of the head hd2.

The head hd2 has a face 5, a hosel 6 and a sole 7. The golf club head hd has a shaft hole 10 to which a shaft is mounted. The shaft hole 10 is formed in the hosel 6.

Materials of the head hd2 and face 5 are not restricted. The face 5 may be a metal, or may be a nonmetal. Examples of the metal include iron, stainless steel, maraging steel, pure titanium, and a titanium alloy. Examples of the iron include soft iron (a low carbon steel having a carbon content of less than 0.3 wt %). Examples of the nonmetal include carbon fiber reinforced plastic (CFRP).

The head hd2 has a plurality of face grooves gv. The face grooves gv are merely also referred to as grooves. A formation method of the face grooves gv is not restricted. Examples of the formation method of the face grooves gv include forging, press processing, casting, and cut processing (carving).

A part of the face 5 is subjected to treatment for adjusting a surface roughness. The typical example of the treatment is shot-blasting treatment. Boundary lines k1 between an area which is subjected to the shot-blasting treatment and an area which is not subjected to the shot-blasting treatment are shown in FIGS. 2 and 3. The boundary lines k1 are a toe side boundary line k1t and a heel side boundary line k1h. An area between the toe side boundary line k1t and the heel side boundary line k1h is subjected to the shot-blasting treatment. All the face grooves gv are formed in the area which is subjected to the shot-blasting treatment. A toe side area relative to the toe side boundary line k1t is not subjected to the shot-blasting treatment. A heel side area relative to the heel side boundary line k1h is not subjected to the shot-blasting treatment. The toe side boundary line kit and the heel side boundary line k1h are visually recognized by the absence or presence of the shot-blasting treatment. The surface roughness is increased by the shot-blasting treatment. The increased surface roughness can increase a backspin rate of a ball. The increase in the backspin rate tends to stop the ball near the point of fall. The increase in the backspin rate can facilitate the stopping of the ball at the aiming point. The increase in the backspin rate is particularly useful for a shot targeting a green and an approach shot. As shown in FIGS. 2 and 3, the boundary layer k1t and the boundary layer k1h are substantially parallel.

The face 5 has a land area LA. The land area LA indicates a portion on which the grooves are not formed, of a surface of the face 5 (face surface). If minute unevenness formed by the shot-blasting treatment or the like is disregarded, the land area LA is substantially a plane.

FIG. 4 shows a cross sectional view taken along line F4-F4 of FIG. 3. A position of the line F4-F4 in a toe-heel direction bisects a distance between a measurement position of a toe side sole width d1 and a measurement position of a heel side sole width d2 (see FIG. 3). A recess part 12 is formed on a back side of the head hd2. The head hd2 is a cavity back type.

As shown in FIG. 4, the head hd2 has a head body 14 and a face plate 16. The head body 14 has an opening (not shown) corresponding to a shape of the face plate 16. The face plate 16 is fitted into the opening. A contour line 18 of the face plate 16 is drawn in FIG. 3.

[Real Loft Angle L1 of Each of Clubs]

The real loft angles L1 of the golf clubs 4 constituting the golf club set 2 are defined as L1(1), L1(2), . . . , L1(n) in an ascending order from the club having the smallest real loft angle L1. In the set 2, the greater the iron number is, the greater the real loft angle L1 is. That is, the set 2 satisfies L1(1)<L1(2)< . . . <L1(n).

The golf club set 2 includes golf clubs 4 having a real loft angle L1 equal to or less than 40 degrees and golf clubs 4 having a real loft angle L1 greater than 40 degrees. In the golf club set 2, the golf clubs 4 having a real loft angle L1 equal to or less than 40 degrees are a 9-iron and clubs (a 4-iron to an 8-iron) having a real loft angle L1 smaller than that of the 9-iron. Another examples of the clubs having a real loft angle L1 equal to or smaller than 40 degrees include a 3-iron, a 2-iron, a 1-iron. In the golf club set 2, the golf clubs 4 having a real loft angle L1 greater than 40 degrees are a pitching wedge and an approach wedge. Another examples of the clubs having a real loft angle L1 greater than 40 degrees include a sand wedge and a lob wedge.

The golf club set 2 includes a golf club having a real loft angle L1 equal to or greater than 50 degrees. The golf club 4 having the real loft angle L1 equal to or greater than 50 degrees is an approach wedge. Another examples of the clubs having a real loft angle L1 of equal to or greater than 50 degrees include a sand wedge and a lob wedge.

A difference between real loft angles L1 of adjacent iron numbers, that is, [L1(m)−L1(m−1)] is usually 2 degrees or greater and 6 degrees or less.

[Measurement Position of Toe Side Sole Width d1]

In the present application, a toe side sole width d1 is defined. A measurement position of the width d1 in a toe-heel direction is a toe side end of the face groove gv (see FIG. 3).

[Measurement Position of Heel Side Sole Width d2]

In the present application, a heel side sole width d2 is defined. A measurement position of the width d2 in a toe-heel direction is a heel side end of the face groove gv (see FIG. 3).

[Measuring Method of Sole Width d1]

FIG. 5 shows a cross sectional view taken along line F5-F5 of FIG. 3. FIG. 5 shows a cross sectional view of the toe side end of the face groove gv. The section is perpendicular to the face surface. The sole width d1 is determined based on a contour line PL1 of the section. In the contour line PL1, a face side end point p1 of the sole 7 is determined. Furthermore, in the contour line PL1, a back side end point b1 of the sole 7 is determined. A distance in a face-back direction between the end point p1 and the end point b1 is the sole width d1.

The end point p1 is a forefront point of the contour line PL1.

The endpoint b1 is defined as follows. When a curvature radius of the contour line PL1 is scanned toward the back side from the center side of the sole 7, a position where the curvature radius is first equal to or less than 10.0 mm is defined as the end point b1.

[Measuring Method of Sole Width d2]

FIG. 6 shows a cross sectional view taken along line F6-F6 of FIG. 3. The section is perpendicular to the face surface. A sole width d2 is determined based on a contour line PL2 of the section. In the contour line PL2, a face side end point p2 of the sole 7 is determined. Furthermore, in the contour line PL2, a backside endpoint b2 of the sole 7 is determined. A distance in a face-back direction between the end point p2 and the end point b2 is the sole width d2.

The end point p2 is a forefront point of the contour line PL2.

The end point b2 is defined as follows. When a curvature radius of the contour line PL2 is scanned toward the back side from the center side of the sole 7, a position where the curvature radius is first equal to or less than 10.0 mm is defined as the end point b2.

In the present application, the toe side sole widths d1 of the plurality of clubs constituting the set are defined as d1(1), d1(2), . . . , d1(n) in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. A maximum value of the toe side sole widths d1 is defined as d1max, and a minimum value of the toe side sole widths d1 is defined as d1min.

For example, in the embodiment of FIG. 1 described above, the toe side sole width d1(1) is a toe side sole width d1 of the 4-iron. The toe side sole width d1(2) is a toe side sole width d1 of the 5-iron. The toe side sole width d1(3) is a toe side sole width d1 of the 6-iron. The toe side sole width d1(4) is a toe side sole width d1 of the 7-iron. The toe side sole width d1(5) is a toe side sole width d1 of the 8-iron. The toe side sole width d1(6) is a toe side sole width d1 of the 9-iron. The toe side sole width d1(7) is a toe side sole width d1 of the pitching wedge. The toe side sole width d1(8) is a toe side sole width d1 of the approach wedge.

In the present application, the heel side sole widths d2 of the plurality of clubs constituting the set are defined as d2(1), d2(2), . . . , d2(n) in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. A maximum value of the heel side sole widths d2 is defined as d2max, and a minimum value of the heel side sole widths d2 is defined as d2min.

For example, in the embodiment of FIG. 1 described above, the heel side sole width d2(1) is a heel side sole width d2 of the 4-iron. The heel side sole width d2(2) is a heel side sole width d2 of the 5-iron. The heel side sole width d2(3) is a heel side sole width d2 of the 6-iron. The heel side sole width d2(4) is a heel side sole width d2 of the 7-iron. The heel side sole width d2(5) is a heel side sole width d2 of the 8-iron. The heel side sole width d2(6) is a heel side sole width d2 of the 9-iron. The heel side sole width d2(7) is a heel side sole width d2 of the pitching wedge. The heel side sole width d2(8) is a heel side sole width d2 of the approach wedge.

In the present application, bounce angles θ1 of the plurality of clubs constituting the set are defined as θ1(1), θ1(2), . . . , θ1(n) in an ascending order of a real loft angle L1 from the club having the smallest real loft angle L1. A maximum value of the bounce angles θ1 is defined as θ1max, and a minimum value of the bounce angles θ1 is defined as θ1min.

For example, in the embodiment of FIG. 1 described above, the bounce angle θ1(1) is a bounce angle θ1 of the 4-iron. The bounce angle θ1(2) is a bounce angle θ1 of the 5-iron. The bounce angle θ1(3) is a bounce angle θ1 of the 6-iron. The bounce angle θ1(4) is a bounce angle θ1 of the 7-iron. The bounce angle θ1(5) is a bounce angle θ1 of the 8-iron. The bounce angle θ1(6) is a bounce angle θ1 of the 9-iron. The bounce angle θ1(7) is a bounce angle θ1 of the pitching wedge. The bounce angle θ1(8) is a bounce angle θ1 of the approach wedge.

[Measurement Position of Bounce Angle θ1]

In the present application, a measurement position of the bounce angle θ1 in the toe-heel direction is a position dv1 bisecting a distance between a measurement position of the toe side sole width d1 and a measurement position of the heel side sole width d2 (see FIG. 3).

[Measuring Method of Bounce Angle θ1]

FIG. 4 shows a cross sectional view taken along line F4-F4 of FIG. 3. The section is perpendicular to the face surface. The bounce angle θ1 is determined based on a contour line PL3 of the section. In the contour line PL3, a face side endpoint p3 of the sole 7 is determined. Furthermore, in the contour line PL3, a back side endpoint b3 of the sole 7 is determined. A distance in a face-back direction between the end point p3 and the end point b3 is a sole width dc.

The end point p3 is a forefront point of the contour line PL3.

The end point b3 is defined as follows. When a curvature radius of the contour line PL3 is scanned toward the back side from the center side of the sole 7, a position where the curvature radius is first equal to or less than 10.0 mm is defined as the end point b3.

A center point Cp is at a position bisecting a distance between the end point p3 and the end point b3 in the face-back direction (see FIG. 4). An angle between a tangent line TL1 of the contour line PL3 at the center point Cp and a level surface h is the bounce angle θ1. The bounce angle θ1 is measured in a head of a base condition. The base condition will be described later.

Preferably, the bounce angle θ1 (degree) satisfies θ1(1)≦θ1(2)≦ . . . ≦θ1(n).

Preferably, the maximum value d1max is substantially equal to the minimum value d1min. The term “substantially equal” means that (d1max−d1min)/d1max is equal to or less than 0.08.

Preferably, the maximum value d2max is substantially equal to the minimum value d2min. The term “substantially equal” means that (d2max−d2min)/d2max is equal to or less than 0.08.

Preferably, a difference (d1max−d1min) is equal to or less than 1.0 mm. More preferably, the difference (d1max−d1min) is equal to or less than 0.8 mm. Still more preferably, the difference (d1max−d1min) is equal to or less than 0.5 mm. Preferably, a lower limit value is equal to or greater than 0 mm, and may be equal to or greater than 0.1 mm in respect of a dimensional error.

Preferably, a difference (d2max−d2min) is equal to or less than 1.0 mm. The difference (d2max−d2min) is more preferably equal to or less than 0.8 mm. The difference (d2max−d2min) is still more preferably equal to or less than 0.5 mm. Preferably, a lower limit value is equal to or greater than 0 mm, and may be equal to or greater than 0.1 mm in respect of a dimensional error.

It was found that novel effects can be produced by suppressing the difference (d1max−d1min) and the difference (d2max−d2min).

A conventional iron set has the following specification A or specification B.

[Specification A]: The greater an iron number is, the wider a sole width is. In other words, the smaller the iron number is, the narrower the sole width is.

[Specification B]: The smaller an iron number is, the wider a sole width is. In other words, the greater the iron number is, the narrower the sole width is.

In the specification A, a sole width of a long iron is narrow, and a sole width of a short iron is wide. On the other hand, in the specification B, a sole width of a long iron is wide, and a sole width of a short iron is narrow. A usual iron set has the specification A.

In the club set, in order to unify a swing balance, the greater the iron number is, the greater a head weight is. Therefore, in the specification B, the smaller the iron number is, the wider the sole width is, and the smaller the head weight is. In this case, in a head having a small iron number, a head weight is small, and weight distribution to a sole is great. Therefore, a weight distributed to a portion other than the sole is small, and a degree of freedom of weight distribution is small. For this reason, a degree of freedom of head design of a head having a small iron number (particularly, a long iron) is small. For example, designs for a position of a center of gravity, a head dimension, and a moment of inertia or the like is constrained.

Since the difference (d1max−d1min) and the difference (d2max−d2min) are restricted in the club set of the embodiment, the constraint of the head having a small iron number to the head design is eased.

The short iron usually tends to be swung with a downward blow. Therefore, influences of a ground on the sole of the short iron are great. When the sole width of the short iron is too wide, ground resistance is excessive, and operativity is apt to be lost. When the sole width of the short iron is too wide, good swinging through is hard to obtain.

Since the difference (d1max−d1min) and the difference (d2max−d2min) are restricted in the club set of the embodiment, a sole width of a short iron having a great iron number is not excessive. Therefore, operativity of the short iron is good, and swinging through is good. The term “good swinging through” means that resistance from the ground is low to be likely to swing a club through.

The long iron usually tends to be swung with a level blow. Therefore, the sole of the long iron is preferably slid on the ground, to hit a ball. When the sole width of the long iron is too narrow, the ball is apt to be duffed.

Since the difference (d1max−d1min) and the difference (d2max−d2min) are restricted in the club set of the embodiment, a sole width of a head having a small iron number is not excessively small. Therefore, the duffing of the long iron is suppressed.

Since the long iron has a long club length and has a small loft, the long iron finds it difficult to hit the ball well. A long iron having a narrow sole width projects an image of thrusting of the long iron into the ground. The long iron having a narrow sole width projects an image of liable duffing. These negative images are apt to induce a misshot. In the embodiment, the sole width of the long iron having a small iron number is not excessively small. Therefore, the misshot can be decreased.

Since the long iron has a small loft in the first place, a height of a suitable trajectory is hard to obtain. In addition, the long iron having a narrow sole width has a high position of a center of gravity. The high position of a center of gravity causes a low trajectory. In the embodiment, the sole width of the long iron having a small iron number is not excessively small. Therefore, the height of the suitable trajectory tends to be obtained.

Many golf players place a sole surface on a ground (lawn) at address. The stability of the head at address is also referred to as “sitting”. The head having stable sitting tends to be stably addressed. When fluctuation between the sittings of the iron numbers is small, the direction of the face at address tends to be stabilized between the iron numbers.

It was found that a difference between the sittings of the different iron numbers is decreased by restricting the difference (d1max−d1min) and the difference (d2max−d2min). For this reason, the direction of the head at address tends to be stabilized. In the head of the embodiment, the face tends to be addressed toward a target in all the iron numbers. It was found that the stability of the sitting causes small variation in hitting directions between different iron numbers.

When a change in the bounce angle and a change in the sole width are overlapped, the difference between the sittings of the different iron numbers may be increased. Even when the bounce angle is changed in the heads of the embodiment, the variation in the sittings between the iron numbers can be suppressed.

In the iron set, “performance flow” is important. The term “performance flow” is performance continuousness between the different iron numbers. Examples of the performance include a flight distance, a trajectory, and a backspin rate. In the iron set, it is preferable that the performance of the club having each of the iron numbers is gradually changed with a change in the iron number. In the iron set, performance suitable for each of the iron numbers tends to be obtained. The iron set having good performance flow facilitates selection of the suitable iron number performed by the golf players. In contrast, it is not preferable that the performance of a certain iron number is projected or a direction of a change in the performance is reversed. The iron set having poor performance flow complicates selection of the suitable iron number performed by the golf players.

Conventionally, in respect of improving the performance flow, it was considered that the sole width is preferably changed with a change in the iron number. However, a change in the sole width and a change in the other specification (a loft angle, a head weight, a club length, a bounce angle, or a position of a center of gravity or the like) are cooperated with each other, and thereby a change in the performance between the adjacent iron numbers tends to be excessive. The excessive change in the performance between the adjacent iron numbers is hardly caused by suppressing the change in the sole width. The club set having good performance flow tends to be obtained by suppressing the change in the sole width.

In respect of the performance flow, a preferable club set satisfies the following formulae (f1) and (f2) or the following formulae (f3) and (f4).

d1(1)≦d1(2)≦ . . . ≦d1(n) (f1)

d2(1)≦d2(2)≦ . . . d2(n) (f2)

d1(1)≧d1(2)≧ . . . d1(n) (f3)

d2(1)≧d2(2)≧ . . . d2(n) (f4)

In respects of suppressing the duffing of the club having a small iron number and of improving the operativity of the club having a great iron number, the bounce angle θ1 (degree) preferably satisfies the following formula (f5), more preferably the following formula (f6), and still more preferably the following formula (f7).

θ1(1)≦θ1(2)≦ . . . θ1(n) (f5)

θ1(1)<θ1(n) (f6)

θ1(1)<θ1(2)< . . . <θ1(n) (f7)

The toe side sole width d1 is not restricted. In respect of suppressing the duffing of the long iron, the toe side sole width d1 is preferably equal to or greater than 18 mm, more preferably equal to or greater than 20 mm, and still more preferably equal to or greater than 23 mm. In respect of the operativity of the short iron, the toe side sole width d1 is preferably equal to or less than 30 mm, more preferably equal to or less than 28 mm, and still more preferably equal to or less than 25 mm.

The heel side sole width d2 is not restricted. In respect of suppressing the duffing of the long iron, the heel side sole width d2 is preferably equal to or greater than 12 mm, more preferably equal to or greater than 14 mm, and still more preferably equal to or greater than 17 mm. In respect of the operativity of the short iron, the heel side sole width d2 is preferably equal to or less than 24 mm, more preferably equal to or less than 22 mm, and still more preferably equal to or less than 19 mm.

A ratio (d1/d2) is not restricted. In respects of suppressing excessive weight distribution to a heel portion and of avoiding an extremely short distance of a center of gravity, the ratio (d1/d2) is preferably equal to or greater than 0.75, more preferably equal to or greater than 1.0, and still more preferably equal to or greater than 1.2. In respects of suppressing excessive weight distribution to a toe portion and of avoiding an extremely long distance of a center of gravity, the ratio (d1/d2) is preferably equal to or less than 2.5, more preferably equal to or less than 2.0, and still more preferably equal to or less than 1.5. These preferable ratios (d1/d2) are preferably satisfied in all the iron numbers. The distance of a center of gravity is a distance between a shaft axis line and a center of gravity of a head.

When the sole width of the long iron is too great, a back side of a sole part can be visually recognized at address. In this case, concentration to the face surface at address may be declined, or an uncomfortable feeling may be produced. In this respect, the heads having all the iron numbers preferably satisfies the follow item (a).

(a) In a toe-heel direction range in which the face surface exists, a top surface of the head is located on the most back side.

When the item (a) is satisfied, the back side of the sole part cannot be viewed at address. Therefore, the concentration to the face surface is facilitated, and the uncomfortable feeling is small. The definitions of a base condition, toe-heel direction, and face-back direction are as follows. The item “back side” described above is judged according to the face-back direction.

[Base Condition]

The base condition is a state where the head is placed on the level surface h at a predetermined lie angle and real loft angle. In more detail, the base condition is the following state. A center axis line z of a shaft hole of a head is provided in an optional vertical surface VP1. The head is grounded on the level surface h in a state where the center axis line z is inclined to the level surface h at a lie angle, and the face surface is inclined to the vertical surface VP1 at a real loft angle (see FIG. 4). The vertical surface VP1 is a plane parallel to a vertical line.

[Toe-Heel Direction]

In the head of the base condition, a direction parallel to an intersection line between the vertical surface VP1 and the level surface h is the toe-heel direction.

[Face-Back Direction]

A direction perpendicular to the toe-heel direction and parallel to the level surface h is the face-back direction.

EXAMPLES

Hereinafter, 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.

Hereinafter, a test was performed using a set having three clubs.

Example 1

Stainless steel was cast, to obtain non-polished heads. Face grooves were formed by cut processing. A sole width and a bounce angle were adjusted by polishing, to obtain heads of example 1. Heads of a 4-iron, 7-iron, and pitching wedge were produced. In all the iron numbers, a sole width between a toe position (a measurement position of a sole width d1) and a heel position (a measurement position of a sole width d2) was gradually narrowed toward a heel side.

A shaft suitable for each of the iron numbers was bonded to each of the heads. “NS PRO 950S” (trade name) manufactured by Nippon Shaft Co., Ltd. was used as the shaft. Grips were mounted to the shafts, to obtain golf clubs according to example 1. A length of the 4-iron was set to 38.5 inches. A length of the 7-iron was set to 37.0 inches. A length of the pitching wedge was set to 35.5 inches.

Examples 2 and 3

The non-polished head obtained in the example 1 was used. A sole width and a bounce angle were adjusted by polishing. Heads according to examples 2 and 3 were obtained in the same manner as in the example 1. In both the examples 2 and 3, in all iron numbers, a sole width between a toe position (a measurement position of a sole width d1) and a heel position (a measurement position of a sole width d2) was gradually narrowed toward a heel side.

The same shaft and grip as those of the example 1 were mounted, to obtain golf clubs according to examples 2 and 3.

Comparative Examples 1 and 2

The non-polished head obtained in the example 1 was used. A sole width and a bounce angle were adjusted by polishing. Heads according to comparative examples 1 and 2 were obtained in the same manner as in the example 1. In both the comparative examples 1 and 2, in all the iron numbers, a sole width between a toe position (a measurement position of a sole width d1) and a heel position (a measurement position of a sole width d2) was gradually narrowed toward a heel side.

The same shaft and grip as those of the example 1 were mounted, to obtain golf clubs according to comparative examples 1 and 2.

Valuation methods are as follows.

[Goodness of Swinging Through]

Ten golf players having a handicap of 0 or greater and 10 or less placed balls on a semi-rough, and actually hit the balls, to evaluate goodness of swinging through. “SRIXON Z-STAR” (trade name) manufactured by SRI Sports Limited was used as the ball. The evaluation is sensuous evaluation. Each of the golf players made five-stage evaluation on a scale of one to five. The score of five is the maximum evaluation, and the score of one is the minimum evaluation. The lower the score is, the lower the evaluation is. The average of the ten golf players' evaluation scores is shown in the following Table 1.

[Ease to Address]

The ten golf players simultaneously evaluated goodness of swinging through and ease to address. The evaluation is sensuous evaluation. Each of the golf players made five-stage evaluation on a scale of one to five. The score of five is the maximum evaluation, and the score of one is the minimum evaluation. The lower the score is, the lower the evaluation is. The average of the ten golf players' evaluation scores is shown in the following Table 1.

[Deviation in Hitting Direction]

The ten golf players placed balls on a fairway, and hit the balls toward a target. Each of the golf players hit five balls using each of iron numbers. “SRIXON Z-STAR” (trade name) manufactured by SRI Sports Limited was used as the ball. A deviation distance (yard) from the target direction was measured. The deviation distance is a distance between a straight line connecting a hitting point to a target point and a final arrival point of the hit ball. The deviation distance was a positive value both in the case where the ball was deviated to a right side and in the case where the ball was deviated to a left side. The average of the ten golf players' measurement values is shown in the following Table 1. Each of the ten golf players is a type to ground a sole surface to address the golf club.

[Hitting Directivity in Set]

A maximum width of deviation in a hitting direction synthesizing three iron numbers was defined as hitting directivity. The hitting directivity was evaluated in four stages of very good, good, average, and poor. These meanings are as follows.

Very Good: Variation in a hitting direction as a whole set is equal to or less than 5 yards.

Good: Variation in a hitting direction as a whole set is greater than 5 yards and equal to or less than 10 yards.

Average: Variation in a hitting direction as a whole set is greater than 10 yards and equal to or less than 15 yards.

Poor: Variation in a hitting direction as a whole set is greater than 15 yards.

The variation in the hitting direction as the whole set was calculated using the test data of the above-mentioned [deviation in hitting direction]. However, the deviation distance was defined as plus when the ball was deviated to a right side. The deviation distance was defined as minus when the ball was deviated to a left side. The average value of the ten golf players' deviation distances was calculated for every iron number. When a maximum value of the deviation distances of the three iron numbers was defined as D1, and a minimum value of the deviation distances of the three iron numbers was defined as D2, a difference (D1−D2) was defined as “variation in a hitting direction as a whole set”.

TABLE 1

specifications and evaluation results of examples and comparative examples

Example
Example
Example
Comparative
Comparative

1
2
3
example 1
example 2

4-iron
Sole width d1 (mm)
24.5
24.0
25.0
30.5
20.0

Sole width d2 (mm)
16.5
16.0
17.0
21.0
17.0

Bounce angle θ1
1.0
1.0
1.0
0.0
0.1

(degree)

Head weight (g)
249.0
247.2
250.8
246.8
239.8

Goodness of swinging
4.0
4.1
3.6
1.8
3.7

through

Ease to address
4.2
4.0
3.9
3.0
1.5

Deviation in hitting
10.8
11.1
10.6
13.6
18.6

direction (yard)

7-iron
Sole width d1 (mm)
24.5
24.5
24.5
28.7
21.0

Sole width d2 (mm)
16.5
16.5
16.5
19.9
16.0

Bounce angle θ1
3.0
3.0
3.0
2.2
1.1

(degree)

Head weight (g)
270.0
270.0
270.0
266.9
263.9

Goodness of swinging
4.1
4.2
3.7
2.8
3.6

through

Ease to address
4.0
4.0
3.9
3.9
2.8

Deviation in hitting
8.6
9.0
8.8
10.1
16.9

direction (yard)

PW
Sole width d1 (mm)
24.5
25.0
24.0
24.1
23.4

Sole width d2 (mm)
16.5
17.0
16.0
18.0
14.8

Bounce angle θ1
5.0
5.0
5.0
7.8
5.8

(degree)

Head weight (g)
294.0
295.7
293.1
290.8
288.9

Goodness of swinging
3.9
3.6
4.0
4.0
3.2

through

Ease to address
3.7
4.2
3.8
1.5
1.4

Deviation in hitting
7.7
8.2
8.0
9.5
8.7

direction (yard)

Hitting directivity in set
Very
Good
Good
Average
Poor

Good

Since fluctuation in sittings between the iron numbers was small in the examples, the variation in the hitting direction was small. Since a difference between the sittings of the iron numbers was small in the examples, evaluation of ease to address was high in all the iron numbers.

As shown in Table 1, the examples are highly evaluated as compared with the comparative examples. From the results, the advantages of the present invention are apparent.

The present invention can be applied to all golf club sets. The description hereinabove is merely for an illustrative example, and various modifications can be made in the scope not to depart from the principles of the present invention.

IRON GOLF CLUB SET

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