Golf club head

The present application claims priorities on Japanese Patent Application No. 2008-197587 filed on Jul. 31, 2008. The whole contents of the Japanese Patent Application are hereby incorporated by reference.

1. Field of the Invention

The present invention relates to a hollow golf club head.

2. Description of the Related Art

A hollow golf club head has been known. The hollow structure increases a head volume and a moment of inertia. A so-called wood type golf club head is usually hollow.

The volume of a hollow part is increased and the thickness of the head is thinned with the increase in size of the head. The head increased in size causes a loud hitting sound.

Golf club heads for obtaining a good hitting sound have been disclosed. As the inventions considering a hitting sound, Japanese Unexamined Patent Application Publication No. 2006-204604 (US2006-172818 A1), Japanese Unexamined Patent Application Publication No. 2008-86351, and Japanese Unexamined Patent Application Publication No. 2005-95247. Japanese Unexamined Patent Application Publication No. 2006-204604 discloses a head having a sole and a rib provided on the inner surface of the sole. The rib has a toe side end and a heel side end which are curved toward a face side relative to a central region.

The hollow golf club head with a great volume has a drawback that a hitting sound is excessively lowered. A higher hitting sound is preferable in order to obtain a good hitting sound. When the rib is provided on the inner surface of the sole, the rigidity of the sole increases and the hitting sound is high. However, in this case, the increase in the weight of the head is caused by the existence of the rib.

It is possible to form a groove on an outer surface of the sole and to form a protruding part at a position on the reverse side of the groove on the inner surface of the sole. The constitution can suppress the increase in the weight and enhance the rigidity of the sole. The enhancement of the rigidity of the sole can improve the hitting sound. However, in this case, stress concentrates on the groove or the protruding part on the reverse side thereof, and the durability is apt to be deteriorated.

It is an object of the present invention to provide a golf club head capable of attaining the improvement of the hitting sound and the enhancement of the durability while suppressing the increase in the weight.

A golf club head according to the present invention has a sole part. The sole part has a groove forming part having a recessed outer surface and a protruding inner surface. The sole part has a first groove forming part and a second groove forming part. The first groove forming part and the second groove forming part have a front-back directional length. A distance between the first groove forming part and the second groove forming part in a toe-heel direction is wider toward a back of the head. The golf club head is hollow.

Preferably, the first groove forming part and the second groove forming part exist on a back of a face surface.

Preferably, the sole part has a connecting groove part formed by connecting a front end of the first groove forming part and a front end of the second groove forming part with each other.

Preferably, a first connecting groove part is provided on a toe side relative to a center section plane of the head, and a second connecting groove part is provided on a heel side relative to the center section plane of the head.

Preferably, a ratio [ta/tb] of a thickness ta (mm) of the groove forming part to an average thickness tb (mm) of the sole part excluding the groove forming part is 1.0 or greater and 2.0 or less.

Preferably, the first groove forming part and the second groove forming part which are adjacent to each other exist.

Preferably, a plurality of sets consisting of the first groove forming part and the second groove forming part exist.

Preferably, an angle θa between an extending direction of the first groove forming part and an extending direction of the second groove forming part adjacent to the first groove forming part is 5 degrees or greater and 60 degrees or less.

Preferably, an angle θt between the groove forming part located closest to a toe side and a front-back direction is 10 degrees or greater and 60 degrees or less; and an angle θh between the groove forming part located closest to a heel side and the front-back direction is 10 degrees or greater and 60 degrees or less.

Preferably, an absolute value of an angle θ 1 between an extending direction of the groove forming part nearest to a center section plane and a front-back direction is 5 degrees or greater and 30 degrees or less.

Preferably, an angle θ 2 between an extending direction of the groove forming part farthest from a center section plane and a front-back direction is 10 degrees or greater and 60 degrees or less.

Preferably, an angle θ 3 between an extending direction of the groove forming part located closest to a toe side and an extending direction of the groove forming part located closest to a heel side is 20 degrees or greater 120 degrees or less.

Preferably, a straight line Lx connects a point on the groove forming part located closest to a front and a point on the groove forming part located closest to a back with each other; and a ratio [m 1 /L 1 ] of a maximum distance m 1 (mm) between a point existing on the groove forming part and the straight line Lx to a length L 1 (mm) of the straight line Lx is equal to or less than 0.5.

Preferably, a height H 1 (mm) of a protruding part on an inner surface side of the groove forming part is 0.1 mm or greater and 3 mm or less.

Preferably, a difference (H 1 −D 1 ) between a height H 1 (mm) of a protruding part on an inner surface side of the groove forming part and a groove depth D 1 (mm) on an outer surface side of the groove forming part is 0.1 mm or greater and 2 mm or less.

Preferably, a groove Mt other than the groove forming part is formed on the sole part; and the groove Mt and the groove forming part are not crossed with each other.

Preferably, a length Lk 1 of the groove forming part is 30 mm or greater and 150 mm or less.

Preferably, a difference [Lk 11 −Lk 12 ] between a length Lk 11 (mm) of the groove forming part nearest to a center section plane on a toe side than the center section plane and a length Lk 12 (mm) of the groove forming part farthest from the center section plane on the toe side than the center section plane is 5 mm or greater and 80 mm or less.

Preferably, a difference [Lk 11 −Lk 12 ] between a length Lk 11 (mm) of the groove forming part nearest to a center section plane on a heel side than the center section plane and a length Lk 12 (mm) of the groove forming part farthest from the center section plane on the heel side than the center section plane is 5 mm or greater and 80 mm or less.

Preferably, a length Lr of the connecting groove part is 100 mm or greater and 200 mm or less.

Preferably, a volume of the head is 350 cc or greater and 460 cc or less.

Preferably, a weight of the head is 170 g or greater and 220 g or less.

FIG. 1 is a view of a golf club head according to an embodiment of the present invention as seen from a crown side;

FIG. 2 is a view of the head of FIG. 1 as seen from a sole side, FIG. 2 substantially equal to a projected image Te to be described later;

FIG. 3 is a cross sectional view taken along a line III-III in FIG. 2 ;

FIG. 4 is a view of the head of FIG. 1 as seen from the sole side;

FIG. 5 is a view of a head according to a second embodiment as seen from a sole side, FIG. 5 substantially equal to the projected image Te;

FIG. 6 is the view of the head according to the second embodiment as seen from the sole side;

FIG. 7 is a view of a head according to a third embodiment as seen from a sole side, FIG. 7 substantially equal to the projected image Te;

FIG. 8 is the view of the head according to the third embodiment as seen from the sole side;

FIG. 9 is a view of a head of Comparative Example 1 as seen from a sole side; and

FIG. 10 is a view of a head of Comparative Example 2 as seen from a sole side.

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

FIG. 1 is a view of a golf club head 2 according to one embodiment of the present invention as seen from a crown side. FIG. 2 is a view of the head 2 as seen from a sole side. FIG. 3 is a cross sectional view of a sole part taken along a line III-III in FIG. 2 . FIG. 4 is a view of the head 2 as seen from the sole side as in FIG. 2 . FIG. 4 is shown in addition to FIG. 2 in order to prevent a large number of reference numerals and auxiliary lines from concentrating.

The head 2 has a face part 4 , a crown part 6 , a sole part 8 , a side part 10 , and a hosel part 12 . The outer surface of the face part 4 is a face surface 13 . The crown part 6 extends toward the backside of the head from the upper edge of the face part 4 . The sole part 8 extends toward the backside of the head from the lower edge of the face part 4 . The side part 10 extends between the crown part 6 and the sole part 8 . As shown in FIG. 4 , the inside of the head 2 is hollow. The head 2 is a hollow golf club head. The head 2 is a so-called wood type golf club head.

The hosel part 12 has a hole 14 to which a shaft is mounted. The shaft (not shown) is inserted into the hole 14 . The hole 14 has a centeral axial line Z 1 (not shown). The centeral axial line Z 1 generally conforms to a shaft axial line of a golf club provided with the head 2 .

In the present invention, a standard perpendicular plane, a front-back direction, a toe-heel direction and a standard projection plane are defined. A standard condition denotes a state that the centeral axial line Z 1 is contained in a plane P 1 perpendicular to a horizontal plane H and the head is placed on the horizontal plane H at a prescribed lie angle and real loft angle. In the standard condition, the standard vertical plane denotes the plane P 1 . In the standard condition, the horizontal plane H is the standard projection plane.

In the present application, the toe-heel direction is a direction of line of intersection between the standard perpendicular plane and the horizontal plane H. In the present application, the front-back direction is a direction perpendicular to the toe-heel direction and parallel to the horizontal plane H.

In the present application, “front” and “front side” are judged on the basis of the front-back direction. In the present application, “back” and “back side” are judged on the basis of the front-back direction. In the present application, “toe side” is judged on the basis of the toe-heel direction. In the present application, “heel side” is judged on the basis of the toe-heel direction.

A plurality of grooves mz 1 are provided on an outer surface g 1 of the sole part 8 . Four grooves mz 1 are provided on the sole part 8 of the head 2 . Recesses are formed on the outer surface g 1 of the sole part 8 by the grooves mz 1 .

As shown in FIG. 3 , protruding parts mz 2 are formed at positions corresponding to the grooves mz 1 on an inner surface s 1 of the sole part 8 . The cross sectional shape of the groove mz 1 is an approximately V shape. The cross sectional shape of the protruding part mz 2 is an approximately V shape. The cross sectional shape of the groove mz 1 and the cross sectional shape of the protruding part mz 2 are approximately equal.

The cross sectional shape of the groove mz 1 is not limited. A rectangle and a semicircle or the like are exemplified as the cross sectional shape of the groove mz 1 . The cross sectional shape of the protruding part mz 2 is not limited. A rectangle and a semicircle or the like are exemplified as the cross sectional shape of the protruding part mz 2 .

The protruding parts mz 2 linearly extend on the inner surface s 1 of the sole part 8 (not shown). The protruding part mz 2 extend along the groove mz 1 on the reverse side of the groove mz 1 (not shown).

The sole part 8 has a groove forming part k 1 having a recessed outer surface g 1 and a protruding inner surface s 1 . A plurality of groove forming parts k 1 are provided. In the head 2 , four groove forming parts k 1 are provided. The outer surface of the groove forming part k 1 forms the groove mz 1 . The inner surface of the groove forming part k 1 forms the protruding part mz 2 .

All the groove forming parts k 1 do not reach the face surface 13 . All the groove forming parts k 1 terminate without reaching the face surface 13 . All the groove forming parts k 1 exist on a back of the face surface 13 . Since the groove forming parts k 1 do not reach the face surface 13 , the groove forming parts k 1 are less likely to be subjected to impact at the time of hitting a ball. Therefore, load on the groove forming parts k 1 can be reduced and the durability of the head 2 can be enhanced.

As shown in FIG. 3 , a thickness ta (mm) of the groove forming part k 1 is approximately equal to an average thickness tb (mm) of the sole part 8 excluding the groove forming part k 1 . In light of hitting sound improving effect and the durability of the groove forming part k 1 , [ta/tb] is preferably equal to or greater than 1.0, more preferably equal to or greater than 1.1, and still more preferably equal to or greater than 1.2. In light of the durability of the sole part 8 and of the suppression of the increase in the weight, [ta/tb] is preferably equal to or less than 2.0, and more preferably equal to or less than 1.5.

The head 2 has a groove forming part k 11 , a groove forming part k 12 , a groove forming part k 13 and a groove forming part k 14 as the groove forming part k 1 . The cross sectional shapes of all the groove forming parts k 1 are common. The groove forming part k 11 is not parallel to the toe-heel direction. Therefore, the groove forming part k 11 has a front-back directional length. Similarly, the groove forming part k 12 has the front-back directional length. The groove forming part k 13 has the front-back directional length. The groove forming part k 14 has the front-back directional length.

The groove forming part k 1 has a front end e 1 and a back end e 2 . All the groove forming parts k 1 have the front end e 1 and the back end e 2 .

The groove forming part k 11 extends linearly. The groove forming part k 12 extends linearly. The groove forming part k 13 extends linearly. The groove forming part k 14 extends linearly.

In the present invention, the sole part 8 has a first groove forming part and a second groove forming part. One of the plurality of groove forming parts k 1 is the first groove forming part. The other one of the plurality of groove forming parts k 1 is the second groove forming part. Any of the plurality of groove forming parts k 1 may be the first groove forming part. Any of the plurality of groove forming parts k 1 may be the second groove forming part. All the groove forming parts excluding the first groove forming part may be the second groove forming part.

In the head 2 , for example, the groove forming part k 11 is the first groove forming part. In the head 2 , for example, the groove forming part k 12 is the second groove forming part. As shown in FIG. 2 , a distance B 1 between the first groove forming part (groove forming part k 11 ) and the second groove forming part (groove forming part k 12 ) in the toe-heel direction is wider toward a back of the head (see FIG. 4 ). That is, the distance B 1 is narrower toward the front of the head.

In the head 2 , for example, the groove forming part k 13 is the second groove forming part. In the head 2 , for example, the groove forming part k 14 is the first groove forming part. As shown in FIG. 2 , a distance B 1 between the first groove forming part (groove forming part k 14 ) and the second groove forming part (groove forming part k 13 ) in the toe-heel direction is wider toward the back of the head (see FIG. 4 ). That is, the distance B 1 is narrower toward a front of the head.

The first groove forming part and the second groove forming part are preferably adjacent to each other. That is, the first groove forming part k 1 and the second groove forming part k 1 are preferably selected so as that another groove forming part does not exist between the first groove forming part and the second groove forming part. For example, in the embodiment of FIG. 4 , the groove forming part k 11 located closest to a toe side may be defined as the first groove forming part k 1 , and the groove forming part k 14 located closest to a heel side may be defined as the second groove forming part k 1 . The distance B 1 between the first groove forming part k 11 and the second groove forming part k 14 in the toe-heel direction is wider toward the back of the head. When the plurality of groove forming parts k 1 exist on the toe side relative to a center section plane Pc, one of the groove forming parts k 1 on the toe side relative to a center section plane Pc is preferably defined as the first groove forming part, and one of the groove forming parts k 1 on the toe side relative to a center section plane Pc is defined as the second groove forming part. When the plurality of groove forming parts k 1 exist on the heel side relative to the center section plane Pc, one of the groove forming parts k 1 on the heel side relative to a center section plane Pc is preferably defined as the first groove forming part, and one of the groove forming parts k 1 on the heel side relative to a center section plane Pc is preferably defined as the second groove forming part.

In the head 2 , a plurality of sets (two sets) consisting of the first groove forming part k 1 and the second groove forming part k 1 exist.

In FIG. 2 , a plane Pc passing through the center of gravity of the head, including a front-back directional line and being perpendicular to the horizontal plane H in the head of the standard condition is shown by a dashed-two dotted line. The plane Pc is the center section plane in the present application.

In the head 2 , the plurality of groove forming parts k 1 exist on the toe side relative to the center section plane Pc. In the head 2 , the groove forming part k 11 and the groove forming part k 12 exist on the toe side relative to the center section plane Pc. In the head 2 , the first groove forming part and the second groove forming part exist on the toe side relative to the center section plane Pc.

In the head 2 , the plurality of groove forming parts k 1 exist on the heel side relative to the center section plane Pc. In the head 2 , the groove forming part k 13 and the groove forming part k 14 exist on the heel side relative to the center section plane Pc. In the head 2 , the first groove forming part and the second groove forming part exist on the heel side relative to the center section plane Pc.

In the head 2 , the plurality of groove forming parts k 1 existing on the toe side relative to the center section plane Pc, and the plurality of groove forming parts k 1 existing on the heel side relative to the center section plane Pc exist. In this case, for example, in a region on the toe side relative to the center section plane Pc, the groove forming part k 1 farthest from the center section plane Pc is defined as the first groove forming part, and the groove forming part k 1 nearest to the center section plane Pc is defined as the second groove forming part. In this case, for example, in a region of the heel side relative to the center section plane Pc, the groove forming part k 1 farthest from the center section plane Pc is defined as the first groove forming part, and the groove forming part k 1 nearest to the center section plane Pc is defined as the second groove forming part.

In the head 2 , in the region of the toe side relative to the center section plane Pc, the distance B 1 between the first groove forming part k 11 and the second groove forming part k 12 in the toe-heel direction is wider toward the back of the head.

In the head 2 , in the region of the heel side relative to the center section plane Pc, the distance B 1 between the first groove forming part k 14 and the second groove forming part k 13 in the toe-heel direction is wider toward the back of the head.

Great stress is apt to act on a portion near the face surface. The distance B 1 is narrower toward the face surface, and thereby the rigidity of the sole can be efficiently enhanced. The distance B 1 is wider toward the back, and thereby the stress acting on the groove forming part k 1 can be efficiently dispersed. Therefore, the distance B 1 is wider toward the back of the head, and thereby the rigidity of the head can be efficiently enhanced. The distance B 1 is wider toward the back of the head, and thereby the load on the bottom of the groove can be reduced and the durability can be enhanced. From this viewpoint, preferably, the sole part does not have a portion in which the distance between the groove forming parts in the toe-heel direction is narrower toward the back of the head.

FIGS. 5 and 6 are views of a head 20 according to a second embodiment as seen from a sole side. The head 20 has a face part (not shown), a crown part (not shown), a sole part 22 , a side part 24 , and a hosel part 26 . The head 20 is the same as the head 2 except for the arrangement of groove forming parts k 1 .

The sole part 22 has connecting groove parts r 1 . Two connecting groove parts r 1 are formed on the sole part 22 .

The connecting groove part r 1 is bent. The connecting groove part r 1 extends toward the front from one end thereof, is folded, extends toward the back, and extends to the other end thereof.

The connecting groove part r 1 is formed by connecting a plurality (two) of groove forming parts k 1 . In the present application, one connecting groove part r 1 is considered to be formed by connecting two groove forming parts k 1 with each other. The connecting groove part r 1 is formed by connecting a front end e 1 of the first groove forming part k 1 and a front end e 1 of the second groove forming part k 1 with each other.

As shown in FIG. 5 , a first connecting groove part r 11 is provided on a toe side relative to a center section plane Pc. A second connecting groove part r 12 is provided on a heel side relative to the center section plane Pc. A first connecting groove part r 1 is provided on the toe side relative to the center of the head 20 in a toe-heel direction. A second connecting groove part r 1 is provided on the heel side relative to the center of the head 20 in the toe-heel direction.

As shown in FIG. 5 , the first connecting groove part r 11 has a first straight line part ts 1 , a second straight line part ts 2 , and a third straight line part ts 3 . In a projected image Te to be described later, the first straight line part ts 1 , the second straight line part ts 2 , and the third straight line part ts 3 extends straightly. The first straight line part ts 1 extends approximately along a front-back direction. The second straight line part ts 2 extends so as that the back side thereof is closer to the toe side. The third straight line part ts 3 connects a front end of the first straight line part ts 1 to a front end of the second straight line part ts 2 . The third straight line part ts 3 extends approximately along the toe-heel direction. All the extending directions of the connecting groove parts are judged in the projected image Te to be described later. The first straight line part ts 1 , the second straight line part ts 2 and the third straight line part ts 3 extends linearly. However, these may extend curvedly.

The second connecting groove part r 12 has a first straight line part ts 4 , a second straight line part ts 5 and a third straight line part ts 6 . In the projected image Te, the first straight line part ts 4 , the second straight line part ts 5 and the third straight line part ts 6 extend straightly. The first straight line part ts 4 extends approximately along the front-back direction. The second straight line part ts 5 extends so as that the back side thereof is closer to the heel side. The third straight line part ts 6 connects a front end of the first straight line part ts 4 to a front end of the second straight line part ts 5 with each other. The third straight line part ts 6 extends approximately along the toe-heel direction. All the extending directions of the connecting groove parts are judged in the projected image Te to be described later. The first straight line part ts 4 , the second straight line part ts 5 and the third straight line part ts 6 extends linearly. However, these may extend curvedly.

The connecting groove part r 1 is divided into the first groove forming part k 1 and the second groove forming part k 1 . The division is carried out by a division line v 1 . The division line v 1 is a straight line which extends in the front-back direction and passes through a dividing point t 1 . The dividing point t 1 is a forefront point of the connecting groove part r 1 . That is, the dividing point t 1 is a point located closest to the front in the connecting groove part r 1 . The term “front” is a front in the front-back direction. When a plurality of points sp 1 located closest to the front exist, a central point cs 1 between a forefront point sp 1 closest to the toe side and a forefront point sp 1 closest to the heel side in the toe-heel direction is defined as the dividing point t 1 . When the central point cs 1 does not exist on the connecting groove part r 1 , a straight line Ls 1 passing through the central point cs 1 and extending in the front-back direction is considered, and a point on the straight line Ls 1 may be defined as the dividing point t 1 . In this case, the straight line Ls 1 agrees to the division line v 1 . The division line v 1 is a virtual line. The division line v 1 is drawn in the projected image Te. The dividing point t 1 is determined in the projected image Te.

In the present application, the extending directions of the groove forming parts and all the angles relating to the groove forming parts are judged in the projected image Te.

The front end e 1 of the first groove forming part k 1 exists on the division line v 1 . The front end e 1 of the second groove forming part k 1 also exists on the division line v 1 .

Thus, the connecting groove part r 1 is divided into the first groove forming part k 1 and the second groove forming part k 1 by the division line v 1 .

FIGS. 7 and 8 are views of a head 30 according to a third embodiment as seen from a sole side. The head 30 has a face part (not shown), a crown part (not shown), a sole part 32 , a side part 34 and a hosel part 36 . The head 30 is the same as the head 2 except for the arrangement of groove forming parts k 1 .

The sole part 32 has connecting groove parts r 1 . Two connecting groove parts r 1 are provided on the sole part 32 . A first connecting groove part r 11 is provided on a toe side relative to a center section plane Pc. A second connecting groove part r 12 is provided on a heel side relative to the center section plane Pc. A first connecting groove part r 1 is provided on the toe side relative to the center of the head 30 in a toe-heel direction. A second connecting groove part r 1 is provided on the heel side relative to the center of the head 30 in the toe-heel direction.

The first connecting groove part r 11 has a first straight line part ts 1 , a second straight line part ts 2 , and a third straight line part ts 3 . In a projected image Te, the first straight line part ts 1 , the second straight line part ts 2 , and the third straight line part ts 3 extends straightly. The first straight line part ts 1 extends so as that the back side thereof is closer to the toe side. The second straight line part ts 2 extends so as that the back side thereof is closer to the toe side. A distance between the first straight line part ts 1 and the second straight line part ts 2 in the toe-heel direction is wider toward the back side. The third straight line part ts 3 connects a front end of the first straight line part ts 1 to a front end of the second straight line part ts 2 . The third straight line part ts 3 extends approximately along the toe-heel direction. All the extending directions of the connecting groove parts are judged in the projected image Te to be described later. The first straight line part ts 1 , the second straight line part ts 2 and the third straight line part ts 3 extend linearly. However, these may extend curvedly.

The second connecting groove part r 12 has a first straight line part ts 4 , a second straight line part ts 5 and a third straight line part ts 6 . In the projected image Te, the first straight line part ts 4 , the second straight line part ts 5 and the third straight line part ts 6 extend straightly. The first straight line part ts 4 extends so as that the back side thereof is closer to the toe side. The second straight line part ts 5 extends so as that the back side thereof is closer to the heel side. A distance between the first straight line part ts 4 and the second straight line part ts 5 in the toe-heel direction is wider toward the back side. The third straight line part ts 6 connects a front end of the first straight line part ts 4 to a front end of the second straight line part ts 5 . The third straight line part ts 6 extends approximately along the toe-heel direction. All the extending directions of the connecting groove parts are judged in the projected image Te to be described later. The first straight line part ts 4 , the second straight line part ts 5 and the third straight line part ts 6 extend linearly. However, these may extend curvedly.

The connecting groove part r 1 is bent. The connecting groove part r 1 extends toward the front side from one end thereof, is folded, extends toward the back side, and extends to the other end thereof.

The connecting groove part r 1 is formed by connecting a plurality (two) of groove forming parts k 1 with each other. In the present application, one connecting groove part r 1 is considered to be formed by connecting two groove forming parts k 1 with each other. The connecting groove part r 1 is formed by connecting a front end e 1 of the first groove forming part k 1 and a front end e 1 of the second groove forming part k 1 with each other.

The front end e 1 of the first groove forming part k 1 exists on the division line v 1 . The front end e 1 of the second groove forming part k 1 also exists on the division line v 1 . The connecting groove part r 1 is divided into the first groove forming part k 1 and the second groove forming part k 1 by the division line v 1 .

In the head 20 and the head 30 , the distance of each of all the connecting groove parts r 1 in the toe-heel direction is wider toward the back. That is, in each of the connecting groove parts r 1 , the distance between the first groove forming part k 1 and the second groove forming part k 1 in the toe-heel direction is wider toward the back side.

In the present application, the extending directions of the groove forming parts and all the angles relating to the groove forming parts are judged in the projected image Te. All the angles shown in FIGS. 4 , 6 and 8 are angles in the projected image Te.

Examples of the angles described in FIGS. 4 , 6 and 8 include an angle θa, an angle θt, an angle θh, an angle θ 1 , an angle θ 2 and an angle θ 3 .

The double-pointed arrow θa shown in FIGS. 4 , 6 and 8 is an angle between the extending direction of the first groove forming part k 1 and the extending direction of the second groove forming part k 1 adjacent to the first groove forming part k 1 . Preferably, the angle θa is an angle formed by two groove forming parts k 1 disposed on the toe side relative to the center section plane Pc. Alternatively, preferably, the angle θa is an angle formed by two groove forming parts k 1 disposed on the heel side relative to the center section plane Pc. The rigidity of the sole part is effectively enhanced by enlarging the angle θa, and thereby the improving effect of the hitting sound can be obtained. When the angle θa is small, two groove forming parts k 1 are nearly in parallel with each other, and stress concentration is apt to occur in the bottom of the groove. The stress concentration is apt to deteriorate the durability. From these viewpoints, the angle θa is preferably equal to or greater than 5 degrees, more preferably equal to or greater than 10 degrees, and still more preferably equal to or greater than 20 degrees. When the extending direction of the groove forming part is close to the toe-heel direction, the groove forming part is apt to be curved by impact caused at the time of hitting a ball. When the deformation of the groove forming part is great, the durability of the groove forming part is apt to be deteriorated. From this viewpoint, the angle θa is preferably equal to or less than 60 degrees, more preferably equal to or less than 50 degrees, and still more preferably equal to or less than 40 degrees, and particularly preferably equal to or less than 30 degrees.

The double-pointed arrow θt shown in FIGS. 4 , 6 and 8 is an angle between the groove forming part k 1 located closest to the toe side and the front-back direction. In light of hitting sound improving effect and durability, the angle θt is preferably equal to or greater than 10 degrees, more preferably equal to or greater than 15 degrees, still more preferably equal to or greater than 20 degrees, and particularly preferably equal to or greater than 30 degrees. In light of suppressing the deformation of the groove forming part to enhance the durability, the angle θt is preferably equal to or less than 60 degrees, more preferably equal to or less than 50 degrees, and still more preferably equal to or less than 40 degrees.

The double-pointed arrow θh shown in FIGS. 4 , 6 and 8 is an angle between the groove forming part k 1 located closest to the heel side and the front-back direction. In light of the hitting sound improving effect and the durability, the angle θh is preferably equal to or greater than 10 degrees, more preferably equal to or greater than 15 degrees, still more preferably equal to or greater than 20 degrees, and particularly preferably equal to or greater than 30 degrees. In light of suppressing the deformation of the groove forming part to enhance the durability, the angle θh is preferably equal to or less than 60 degrees, more preferably equal to or less than 50 degrees, and still more preferably equal to or less than 40 degrees.

The double-pointed arrow θ 1 shown in FIGS. 6 and 8 is an angle between the extending direction of the groove forming part k 1 closest to the center section plane Pc and the front-back direction when the head is divided by the center section plane Pc. The angle θ 1 may be 0 degree. In light of alleviating the stress concentration in the face side end part of the groove forming part k 1 , the absolute value of the angle θ 1 is preferably equal to or greater than 5 degrees, and more preferably equal to or greater than 10 degrees. In light of the groove forming part k 1 closest to the center section plane Pc among the groove forming parts k 1 located on the toe side relative to the center section plane Pc, and the groove forming part k 1 closest to the center section plane Pc among the groove forming parts k 1 located on the heel side relative to the center section plane Pc being separated as approaching the back side of the head, the angle θ 1 is preferably equal to or greater than 5 degrees, and preferably equal to or greater than 10 degrees. When the angle θ 1 is excessively great, the stress concentration is apt to occur in the bottom of the groove. When the angle θ 1 is excessively great, an angle θ 2 to be described later is easily set to a preferable value. From this viewpoint, the angle θ 1 is preferably equal to or less than 30 degrees, more preferably equal to or less than 20 degrees, and still more preferably equal to or less than 15 degrees. In light of efficiently enhancing the rigidity of the sole part, the extending direction of the groove forming part k 1 near the center section plane Pc is preferably inclined so as that the back thereof is away from the center section plane Pc when the head is divided by the center section plane Pc.

When the extending direction of the groove forming part k 1 is separated from the center section plane Pc as approaching the back side, the angle θ 1 is defined as a plus value. On the other hand, when the extending direction of the groove forming part k 1 is separated from the center section plane Pc as approaching the front side, the angle θ 1 is defined as a minus value. In the embodiment of FIG. 6 , both the angles θ 1 of two positions are minus. In the embodiment of FIG. 8 , both the angles θ 1 of two positions are plus. Referring to the angle θh and the angle θt, plus and minus are defined as well as the angle θ 1 . In the embodiment of FIG. 4 , the angle θh is plus and the angle θt is also plus.

The double-pointed arrow θ 2 shown in FIGS. 6 and 8 is an angle between the extending direction of the groove forming part k 1 farthest from the center section plane Pc and the front-back direction when the head is divided by the center section plane Pc. In light of setting the angle θ 1 to a preferable value, the angle θ 2 is preferably equal to or greater than 10 degrees, more preferably equal to or greater than 15 degrees, still more preferably equal to or greater than 20 degrees, and particularly preferably equal to or greater than 30 degrees. In light of suppressing the deformation of the groove forming part to enhance the durability, the angle θ 2 is preferably equal to or less than 60 degrees, more preferably equal to or less than 50 degrees, and still more preferably equal to or less than 40 degrees. In light of efficiently enhancing the rigidity of the sole part to improve the hitting sound, the extending direction of the groove forming part k 1 far from the center section plane Pc is preferably inclined so as that the back side thereof is away from the center section plane Pc when the head is divided by the center section plane Pc.

When the extending direction of the groove forming part k 1 is separated from the center section plane Pc as approaching the back side, the angle θ 2 is defined as a plus value. On the other hand, when the extending direction of the groove forming part k 1 is separated from the center section plane Pc as approaching the front side, the angle θ 2 is defined as a minus value. In the embodiments of FIGS. 6 and 8 , both the angles θ 2 of two positions are plus.

The double-pointed arrow θ 3 shown in FIGS. 4 , 6 and 8 is an angle between the extending direction of the groove forming part k 1 located closest to the toe side and the extending direction of the groove forming part k 1 located closest to the heel side. In light of efficiently enhancing the rigidity of the sole part to improve the hitting sound, the angle θ 3 is preferably equal to or greater than 20 degrees, more preferably equal to or greater than 30 degrees, still more preferably equal to or greater than 40 degrees, and particularly preferably equal to or greater than 60 degrees. In light of suppressing the deformation of the groove forming part to enhance the durability, the angle θ 3 is preferably equal to or less than 120 degrees, more preferably equal to or less than 100 degrees, and still more preferably equal to or less than 80 degrees.

In the embodiment of FIG. 6 and the embodiment of FIG. 8 , the groove forming parts k 1 are bent. An extending direction En of the groove forming part k 1 is defined as follows, including the case where the groove forming parts k 1 are bent. In the projected image Te, a straight line Lx which connects a point on the groove forming part k 1 located closest to the front side and a point on the groove forming part k 1 located closest to the back side with each other is defined. The direction of the straight line Lx is the extending direction En. When the connecting groove part r 1 is formed by connecting the groove forming parts k 1 , a straight line which connects a point located closest to the back and a dividing point t 1 with each other is the straight line Lx. The direction of this straight line Lx is the extending direction En. The straight line Lx is contained in a straight line drawn as the extending direction En in FIGS. 4 , 6 and 8 .

A maximum distance between a point which exists on the groove forming part k 1 and the straight line Lx is shown by a double-pointed arrow m 1 in FIG. 6 . A length (mm) of the straight line Lx is shown by a double-pointed arrow L 1 in FIG. 6 . The distance m 1 and the length L 1 are determined in the projected image Te. When the groove forming parts k 1 are bent, the distance m 1 (mm) is greater than 0. In light of further enhancing effects relating to the angles (angle θ 1 , angle θ 2 , angle θ 3 , angle θa, angle θt, and angle θh), a ratio [m 1 /L 1 ] of the distance m 1 to the length L 1 is considered. The effects relating to the angles can be enhanced with the smaller ratio [m 1 /L 1 ] when the groove forming parts r 1 are bent. From this viewpoint, the ratio [m 1 /L 1 ] is preferably equal to or less than 0.5, more preferably equal to or less than 0.3, and still more preferably equal to or less than 0.1.

A depth (mm) of a groove on the outer surface side of the groove forming part is shown by a double-pointed arrow D 1 in FIG. 3 . In light of enhancing the hitting sound improving effect, the depth D 1 is preferably equal to or greater than 0.1 mm, more preferably equal to or greater than 0.3 mm, and still more preferably equal to or greater than 0.5 mm. In light of the durability of the groove forming part, the depth D 1 is preferably equal to or less than 3 mm, more preferably equal to or less than 2 mm, and still more preferably equal to or less than 1 mm.

A height (mm) of the protruding part on the inner surface side of the groove forming part is shown by a double-pointed arrow H 1 in FIG. 3 . In light of enhancing the hitting sound improving effect, the height H 1 is preferably equal to or greater than 0.1 mm, more preferably equal to or greater than 0.3 mm, and still more preferably equal to or greater than 0.5 mm. In light of the durability of the groove forming part, the height H 1 is preferably equal to or less than 3 mm, more preferably equal to or less than 2 mm, and still more preferably equal to or less than 1 mm.

In light of the durability and the hitting sound improving effect, the thickness of the groove forming part is preferably greater than that of the sole part around the groove forming part. From this viewpoint, the height H 1 is preferably greater than the depth D 1 . Specifically, a difference (H 1 −D 1 ) between H 1 and D 1 is preferably equal to or greater than 0.1 mm. In light of suppressing the increase in the weight, the difference (H 1 −D 1 ) is preferably equal to or less than 2 mm, more preferably equal to or less than 1 mm, and still more preferably equal to or less than 0.5 mm.

A groove Mt (not shown) other than the groove forming part may be formed on the sole part. Preferably, the groove forming part and the groove Mt are not crossed with each other. When the groove forming part and the groove Mt are crossed with each other, cracks or the like are apt to be created in the crossing portion. In the same viewpoint, preferably, the groove forming parts are not crossed with each other.

A length Lk 1 (not shown) of the groove forming part is not limited. In light of the hitting sound improving effect, the length Lk 1 is preferably equal to or greater than 30 mm, more preferably equal to or greater than 40 mm, still more preferably equal to or greater than 50 mm, and particularly preferably equal to or greater than 70 mm. In light of the durability of the groove forming part and of the suppression of the weight of the head, the length Lk 1 is preferably equal to or less than 150 mm, more preferably equal to or less than 120 mm, and still more preferably equal to or less than 100 mm. When the groove forming parts are bent, the length Lk 1 is measured along the bent direction. When the connecting groove part is provided, the length Lk 1 is a length between the division line v 1 and the back end of the groove forming part.

The central part of the sole part is apt to vibrate as compared with the peripheral part of the sole part. The hitting sound is likely to be more effectively improved by providing the groove forming part on the central part of the sole part. From this viewpoint, a length Lk 11 (mm) of the groove forming part closest to the center section plane Pc on the toe side relative to the center section plane Pc is preferably longer than a length Lk 12 (mm) of the groove forming part farthest from the center section plane Pc on the toe side relative to the center section plane Pc. Similarly, the length Lk 11 of the groove forming part closest to the center section plane Pc on the heel side relative to the center section plane Pc is preferably longer than the length Lk 12 of the groove forming part farthest from the center section plane Pc on the heel side relative to the center section plane Pc. Specifically, a difference [Lk 11 −Lk 12 ] is preferably equal to or greater than 5 mm, more preferably equal to or greater than 10 mm, and still more preferably equal to or greater than 20 mm. When the length Lk 12 is excessively short, the hitting sound improving effect may be deteriorated. From this viewpoint, the difference [Lk 11 −Lk 12 ] is preferably equal to or less than 80 mm, more preferably equal to or less than 60 mm, and still more preferably equal to or less than 40 mm.

A length Lr (not shown) of the connecting groove part is not limited. In light of the hitting sound improving effect, the length Lr is preferably equal to or greater than 100 mm, more preferably equal to or greater than 120 mm, still more preferably equal to or greater than 130 mm. In light of the durability of the connecting groove part and of the suppression of the weight of the head, the length Lr is preferably equal to or less than 200 mm, more preferably equal to or less than 180 mm, and still more preferably equal to or less than 160 mm. When the connecting groove part is bent, the length Lr is measured along the bent direction.

When the volume of the head is great, the thickness of the head is apt to be thinned. Since the rigidity of the head is low when the thickness of the head is thin, the effects of the present invention obtained by the groove forming part are high. From this viewpoint, the volume of the head is preferably equal to or greater than 350 cc, more preferably equal to or greater than 380 cc, and still more preferably equal to or greater than 400 cc. In light of being compliant with the Golf Rules, the volume of the head is preferably equal to or less than 460 cc.

In light of a great moment of inertia enhancing the directionality of the ball, the weight of the head is preferably equal to or greater than 170 g, more preferably equal to or greater than 180 g, and still more preferably equal to or greater than 190 g. In light of obtaining the golf club which having an optimum club balance and being easily swung, the weight of the head is preferably equal to or less than 220 g, and more preferably equal to or less than 210 g.

The material for the head is not limited. As the material for the head, metal and CFRP (Carbon Fiber Reinforced Plastic) or the like are exemplified. As the metal used for the head, one or more kinds of metals selected from pure titanium, a titanium alloy, stainless steel, maraging steel, an aluminium alloy, Zr metal glass, carbon steel, Fe—Al—Mn alloy, a magnesium alloy and a tungsten-nickel alloy are exemplified. As the titanium alloy, 6-4 titanium (Ti-6Al-4V) and Ti-15V-3Cr-3Sn-3Al or the like are exemplified.

A method for manufacturing the head is not particularly limited. Usually, a hollow head is manufactured by bonding two or more members. A method for manufacturing the members constituting the head is not limited. As the method, casting, forging and press forming are exemplified. In casting, lost wax precision casting is preferable.

Examples of the structures of the heads include a two-piece structure in which two members integrally formed respectively are bonded, a three-piece structure in which three members integrally formed respectively are bonded, and a four-piece structure in which four members integrally formed respectively are bonded.

The following items are exemplified as the method for manufacturing the head.

(1) A head obtained by bonding a head body made of stainless steel and formed by casting, and a face member made of a titanium alloy by brazing. (2) A head obtained by bonding a head body made of stainless steel and formed by casting, a face member made of a titanium alloy, and a crown member made of a titanium alloy by brazing. (3) A head obtained by bonding a head body made of stainless steel and formed by casting, and a face member made of maraging steel by welding. (4) A head obtained by bonding a head body made of stainless steel and formed by casting, and a crown member made of a carbon fiber reinforced plastic by an adhesive. (5) A head obtained by bonding a head body made of stainless steel and formed by casting, and a crown member made of a magnesium alloy by an adhesive. (6) A head obtained by bonding a head body made of a titanium alloy and formed by casting, and a face member made of a titanium alloy by welding. (7) A head obtained by bonding a head body made of a titanium alloy and formed by casting, a face member made of a titanium alloy, and a crown member made of a titanium alloy by welding. (8) A head obtained by welding a head body made of a titanium alloy and formed by casting and a face member made of a titanium alloy, and further bonding the head body and a crown member made of a carbon fiber reinforced plastic by an adhesive. (9) A head obtained by welding a head body made of a titanium alloy and formed by casting and a face member made of a titanium alloy, and further bonding the head body and a crown member made of a magnesium alloy by an adhesive. (10) A head obtained by bonding a head body made of a titanium alloy and formed by casting, and a face member made of a magnesium alloy by an adhesive. (11) A head obtained by bonding a head body made of a titanium alloy and formed by casting, and a crown member made of a carbon fiber reinforced plastic by an adhesive. A plate-shaped face member and a cup-shaped face member are exemplified as the form of the face member.

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 Examples.