GOLF CLUB HEAD

Abstract

Provided is a golf club head that includes a face portion for hitting a ball. The face portion has a thick portion that includes a face center, and a peripheral portion that is thinner than the thick portion and surrounds the thick portion. The thick portion extends along a central axis line, and has a recessed portion on at least one side of the central axis line so that a central region of the thick portion along the central axis line is recessed more toward the central axis line than parts of the thick portion on two sides of the central region along the central axis line. Note that the central axis line extends in a top-sole direction or in a direction inclined from a toe side toward a heel side along a direction from a sole side toward a top side.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims a priority to Japanese Patent Application No. 2015-113364 filed on Jun. 3, 2015, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

The present invention relates to a golf club head.

BACKGROUND

Conventionally, various innovations have been made with respect to the design of the thickness of the face portion of a golf club head from the viewpoint of strength, the viewpoint of extending the flight-distance, and the like. In general, from the viewpoint of ensuring strength, it can be said that a thicker face portion is better, but from the viewpoint of extending the flight-distance, it is important to reduce the thickness of the face portion to improve the restitution performance. JP 2010-530783A discloses a golf club head in which the central region of the face portion, which normally receives the most impact when hitting a ball, is formed with a high thickness, and the peripheral region thereof is formed with a low thickness. In this golf club head, the thick portion in the central region is formed with an approximately elliptical shape.

SUMMARY of INVENTION

Incidentally, improvement in flight-distance is a never-ending goal for golfers. On the other hand, it is also necessary to ensure strength for the golf club head. In view of this, the inventor of the present invention sought a method for further improving flight-distance while also ensuring strength for the golf club head through an innovation in the thickness design.

An object of the present invention is to provide a golf club head that can extend the flight-distance while also ensuring strength.

A golf club head according to a first aspect of the present invention is a golf club head that includes a face portion for hitting a ball. The face portion has a thick portion that includes a face center, and a peripheral portion that is thinner than the thick portion and surrounds the thick portion. The thick portion extends along a central axis line, and has a recessed portion on at least one side of the central axis line so that a central region of the thick portion along the central axis line is recessed more toward the central axis line than parts of the thick portion on two sides of the central region along the central axis line. Note that the central axis line extends in a top-sole direction or in a direction inclined from a toe side toward a heel side along a direction from a sole side toward a top side.

A golf club head according to a second aspect of the present invention is the golf club head according to the first aspect, wherein the thick portion has the recessed portion on each side of the central axis line.

A golf club head according to a third aspect of the present invention is the golf club head according to the second aspect, wherein the recessed portions on both sides of the central axis line oppose each other across the central axis line.

A golf club head according to a fourth aspect of the present invention is the golf club head according to any of the first to third aspects, wherein the central axis line is a line segment having a maximum length among line segments that pass through a centroid of the thick portion and are overlapped with the thick portion, and intersects a boundary line of the thick portion at a first intersection and a second intersection. The face portion includes a hit point distribution region. The hit point distribution region is surrounded by a first orthogonal line that passes through the first intersection and is orthogonal to the central axis line, a second orthogonal line that passes through the second intersection and is orthogonal to the central axis line, and a boundary line of the face portion. A groove that extends along the boundary line of the face portion and is at least partially overlapped with the hit point distribution region is formed on a back surface side of the face portion.

A golf club head according to a fifth aspect of the present invention is the golf club head according to the fourth aspect, wherein the boundary line of the face portion includes a top line on a top side that extends between a toe-side end point, being a point farthest on a toe side, and a heel-side end point, being a point farthest on a heel side, and includes a sole line on a sole side that extends between the toe-side end point and the heel-side end point. The hit point distribution region has a first corner point on a toe side and a second corner point on a heel side on the top line, and has a third corner point on a toe side and a fourth corner point on a heel side on the sole line. The groove includes at least one of a toe-side groove and a heel-side groove. The toe-side groove extends at least from the first corner point into the hit point distribution region along the boundary line of the face portion but does not reach the second corner point, and the heel-side groove extends at least from the fourth corner point into the hit point distribution region along the boundary line of the face portion but does not reach the third corner point.

A golf club head according to a sixth aspect of the present invention is the golf club head according to the fifth aspect, wherein the groove includes both the toe-side groove and the heel-side groove.

A golf club head according to a seventh aspect of the present invention is the golf club head according to the fifth aspect or the sixth aspect, having a volume of 400 cubic centimeters or more.

A golf club head according to an eighth aspect of the present invention is the golf club head according to the fourth aspect, wherein the boundary line of the face portion includes a sole line on a sole side that extends between a toe-side end point, being a point farthest on a toe side, and a heel-side end point, being a point farthest on a heel side. The groove extends along the sole line.

A golf club head according to a ninth aspect of the present invention is the golf club head according to the eighth aspect, having a volume less than 400 cubic centimeters.

Generally, hit points on a face portion are distributed around a straight line (referred to hereinafter as the actual hit point distribution line) that passes through the face center region and is inclined from the heel side toward the toe side along the direction from the sole side toward the top side. On the other hand, the face portion of the golf club head according to the present invention is provided with a thick portion that includes the face center and extends along a central axis line that intersects the actual hit point distribution line. Accordingly, the face center region is thick, thus ensuring strength. Also, the thick portion is provided with a recessed portion on at least one side of the central axis line so that the central region of the thick portion along the central axis line recedes more toward the central axis line than the parts of the thick portion on the two sides of the central region along the central axis line. In other words, the thick portion is recessed in the direction in which the actual hit point distribution line extends, and thus the thin region spreads out so as to conform to the actual hit point distribution line. As a result, the high restitution factor area spreads out along the actual hit point distribution region, and it is possible to improve the flight-distance. Accordingly, it is possible to extend the flight-distance while also ensuring strength for the golf club head.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a golf club head according to a first embodiment in a reference state;

FIG. 2 is a plan view of the golf club head in the reference state;

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

FIG. 4 is a front view of the golf club head in the reference state;

FIG. 5 is a front view of a face portion of a golf club head according to a second embodiment in a reference state;

FIG. 6 is a front view of a face portion of a golf club head according to a variation in the reference state;

FIG. 7 is a front view of a face portion of a golf club head according to another variation in the reference state; and

FIG. 8 is a front view of the golf club head according to the first embodiment in the reference state, and shows an actual hit point distribution region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Golf club heads according to several embodiments of the present invention will be described below with reference to the drawings.

1. First Embodiment

1-1. Overview of Golf Club Head

FIG. 1 is a perspective view of a golf club head (hereinafter sometimes simply referred to as the “head”) 100 of the present embodiment in a reference state, and FIG. 2 is a plan view of the head 100 in the reference state. The reference state of the golf club head will be described later. The head 100 is a hollow structure and has wall surfaces formed by a face member 1, a crown portion 2, a sole portion 3, a side portion 4, and a hosel portion 5. The head 100 of the present embodiment is a driver (#1).

The face member 1 constitutes a front portion of the head 100 that serves as the surface for hitting a ball. The crown portion 2 is adjacent to the face member 1 and constitutes the upper surface of the head 100. The sole portion 3 constitutes the bottom surface of the head 100, and is adjacent to the face member 1 and the side portion 4. Also, the side portion 4 is the portion between the crown portion 2 and the sole portion 3, and extends from the toe side of the face member 1, across the back side of the head 100, to the heel side of the face member 1. Furthermore, the hosel portion 5 is the portion provided adjacent to the heel side of the crown portion 2, and has an insertion hole 51 for the insertion of the shaft (not shown) of the golf club. A central axis Z of the insertion hole 51 conforms to the axis of the shaft.

The following describes the aforementioned reference state. As shown in FIGS. 1 and 2, the reference state is defined as a state in which the central axis Z is in a plane (hereinafter, the reference vertical plane) P that is perpendicular to a horizontal plane H (see FIG. 3), and furthermore the head is placed on the horizontal plane H at a predetermined lie angle and real loft angle. Also, as shown in FIG. 2, the direction of the line of intersection of the reference vertical plane P and the horizontal plane H will be referred to as the toe-heel direction, and the direction that is perpendicular to the toe-heel direction and parallel to the horizontal plane H will be referred to as the face-back direction. Also, the direction perpendicular to the horizontal plane H will be referred to as the top-sole direction. Note that in the description of the present embodiment, unless otherwise stated, “forward-rear” means the face-back direction, the “face side” is forward, and the “back side” is rearward. Also, unless otherwise stated, “up-down” refers to the top-sole direction, the “top side” is upward, and the “sole side” is downward.

The head 100 can be formed from a titanium alloy having a specific gravity of approximately 4.4 to 5.0 (e.g., Ti-6Al-4V), for example. Besides a titanium alloy, the head can be formed from one or two or more materials selected from among stainless steel, maraging steel, an aluminum alloy, a magnesium alloy, an amorphous alloy, and the like. Also, there is no limitation to a metal material, and the head can also be formed using a fiber-reinforced plastic or the like. Moreover, it is preferable that the volume of the head 100, which is a driver, is 400 cubic centimeters or more.

The head 100 of the present embodiment is constituted by assembling the face member 1 with a head body 6 that is a hollow structure having the crown portion 2, the sole portion 3, the side portion 4, and the hosel portion 5. The head body 6 and the face member 1 are joined by welding (TIG (Tungsten-Inactive Gas) welding, plasma welding, laser welding, brazing, etc.), for example. The head body 6 has an opening on the front side surrounded by the crown portion 2, the sole portion 3, and the side portion 4, and the face member 1 is attached so as to block this opening. The head body 6 can also be an assembly of multiple parts, and can also be formed as a single body. The head body 6 and the face member 1 can be produced using various methods. For example, the head body 6 can be manufactured by casting using a known lost-wax precision casting method or the like. Also, the face member 1 can be manufactured using a forging method, flat plate press machining, casting, or the like. Note that the component configuration of the head 100 described here is an illustrative example, and it can also be an assembly of multiple components different from this example, and can also be formed as a single body.

Hereinafter, the face member 1 will be described with reference to FIG. 3 as well. FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2. As shown in FIGS. 1 to 3, the face member 1 of the present embodiment is of the so-called “cup face” type. In other words, the face member 1 is shaped as a cup that has a flat plate-shaped face portion 11 for hitting a ball and a rising portion (extending portion) 12 that extends rearward from the peripheral edge of the face portion 11.

This cup face-type face member 1 has a higher restitution factor in the face portion 11 than a face member not having a rising portion, because the area of flexure is larger by an amount corresponding to the rising portion 12. Also, in the case where the cup face construction is employed, the connection portion of the face member 1 and the head body 6, where rigidity tends to increase, moves rearward of the face portion 11, and therefore the overall face portion 11 flexes easily. Accordingly, the cup face construction contributes to an increase in flight-distance.

Additionally, various innovations have been made to the golf club head 100 in order to improve the restitution factor of the face portion 11 for the purpose of increasing the flight-distance. Specifically, a characteristic structure has been formed in the vicinity of the connection portion of the face member 1 and the head body 6, and an innovation has also been made to the thickness structure of the crown portion 2 and the face portion 11. These features will be described below in order.

1-2. Structure in Vicinity of Connection Portion of Face Member and Head Body

As shown in FIGS. 1 and 2, a front edge portion 20 of the crown portion 2 has a protruding shape in which a central region thereof projects forward. Specifically, the front edge portion 20 of the crown portion 2 has a first toe-side portion 20a that is on the toe side, a first heel-side portion 20b that is on the heel side, and a first central portion 20c located between the portions 20a and 20b, and the first central portion 20c projects forward more than the first toe-side portion 20a and the first heel-side portion 20b. On the other hand, in the rising portion 12 of the face member 1, the portion fixed to the front edge portion 20 of the crown portion 2 (hereinafter, the fixed portion being referred to as the “upper rising portion 30”) has a structure that corresponds to the above-described structure of the crown portion 2. Specifically, in the upper rising portion 30, the two side regions have a protruding shape of projecting rearward, and the central region has a receding shape of being recessed forward. Specifically, the upper rising portion 30 has a second toe-side portion 30a that is joined to the first toe-side portion 20a, a second heel-side portion 30b that is joined to the first heel-side portion 20b, and a second central portion 30c that is joined to the first central portion 20c. Also, the second toe-side portion 30a and the second heel-side portion 30b project rearward more than the second central portion 30c. Note that the second central portion 30c is the portion located between the second toe-side portion 30a and the second heel-side portion 30b.

The protruding shape of the front edge portion 20 of the crown portion 2 and the protruding shape of the upper rising portion 30 of the face member 1 contribute to an enlargement of the high restitution area on the face portion 11. Specifically, the connection portion of the face member 1 and the head body 6 recedes rearward on the toe side and the heel side, and thus the amount of flexure during ball-hitting increases in the toe-side and heel-side portions of the face portion 11, and therefore the restitution factor improves in the face portion 11 overall.

1-3. Thickness Structure of Face Portion

Next, the thickness structure of the face portion 11 that contributes to an increase in the flight-distance will be described. The front surface (hereinafter, called the face surface) side of the face portion 11 that serves as the ball hitting face is formed so as to be smooth and flat. On the other hand, unevenness is formed on the back surface side of the face portion 11. In other words, the face portion 11 is constituted by multiple regions having different thicknesses.

FIG. 4 is a front view of the head 100 in the reference state. Accordingly, it would not actually be possible to see the thickness structure formed on the inner surface of the face portion 11 in this figure. However, in consideration of facilitating understanding, the thickness structure is shown in the figure. As shown in FIG. 4, a thick portion 50 is formed in the central region of the face portion 11, and a peripheral portion 60 that is thinner than the thick portion 50 is formed so as to surround the thick portion 50. The peripheral portion 60 has an approximately ring-shaped transition portion 61 that surrounds the thick portion 50 and comes into contact with the thick portion 50, and thin portions 62a and 62b that further surround the transition portion 61 and come into contact with the transition portion 61. The transition portion 61 is thicker than the thin portions 62a and 62b, but is thinner than the thick portion 50. The thin portions 62a and 62b are separated on the toe side and the heel side respectively, with the transition portion 61 therebetween, the thin portion 62a is the region on the heel side of the transition portion 61, and the thin portion 62b is the region on the toe side of the transition portion 61. In the present embodiment, the transition portion 61 is constituted so as to gradually decrease in thickness from the thick portion 50 toward the outside, that is to say toward the thin portions 62a and 62b, and this change in thickness is continuous. However, the thicknesses of the transition portion 61 may be constant, and even in the case of changing, the thicknesses may change in a non-continuous manner, such as in a stepwise manner.

As shown in FIG. 3, in the present embodiment, a thickness w1 of the thick portion 50 is approximately constant and can be preferably set to 2.0 mm≦w1≦4.5 mm or more preferably 3.0 mm≦w1≦4.0 mm, and in the present embodiment, w1=3.65 mm. Also, in the present embodiment, a thickness w2 of the thin portions 62a and 62b is also approximately constant and can be preferably set to 1.5 mm≦w2≦3.0 mm or more preferably 1.8 mm≦w2≦2.6 mm, and in the present embodiment, w2=2.00 mm.

Hereinafter, for the sake of convenience in the description, assuming that the head 100 is placed in the reference state, a point Pt farthest on the toe side on the peripheral edge of the face portion 11 (the boundary line between the face portion 11 and the rising portion 12) will be referred to as the toe-side end point, and a point Ph farthest on the heel side will be referred to as the heel-side end point. Also, on the peripheral edge of the face portion 11, the top-side line extending from the toe-side end point Pt to the heel-side end point Ph will be referred to as a top line L1, and a sole-side line extending from the toe-side end point Pt to the heel-side end point Ph will be referred to as a sole line L2. Furthermore, a central axis line L3 is defined that is inclined from the toe side to the heel side along the direction from the sole side to the top side on the face surface. In the present embodiment, the central axis line L3 is the line segment that passes through a centroid Pw (geometrical center) of the thick portion 50 on the face surface, overlaps the thick portion 50, and has a maximum length. An angle θ1 formed by the central axis line L3 and the toe-heel direction can be preferably set to 5°≦θ1<90° or more preferably 30°≦θ1≦60°, for example.

As shown in FIG. 4, the thick portion 50 includes a face center Pc and a sweet spot located in the vicinity thereof, and extends in an “I” shape along the central axis line L3. Note that the “I” shape in the present specification refers to a shape that extends along one straight line. The thick portion 50 of the present embodiment reaches neither the top line L1 nor the sole line L2. Here, the face center Pc is specified as follows. Specifically, first, in the face portion, a maximum width Wx in the toe-heel direction is determined, and a central position Px in the toe-heel direction at the maximum width Wx is determined. Then, at the position Px, a central point Py in the up-down direction of the face portion is determined, and this point Py is defined as a face center Pc. Note that FIG. 3 is a cross-sectional view that passes through the face center Pc. Also, the sweet spot is the foot of the perpendicular line from the center of gravity of the golf club head 100 to the face portion 11. Moreover, although the centroid Pw of the thick portion 50 matches the face center Pc in the present embodiment, the points Pc and Pw do not need to match. It should be noted that it is preferable that the points Pc and Pw are arranged in the vicinity of each other.

In a front view, the thick portion 50 has recessed portions 51a and 51b on respective sides of the central axis line L3. The recessed portions 51a and 51b are each a portion formed due to the central region of the thick portion 50 along the central axis line L3 being more recessed toward the central axis line L3 than the parts of the thick portion 50 on the two sides of the central region along the central axis line L3. Here, the recessed portion 51a is located more toward the heel side, and the recessed portion 51b is located more toward the toe side. In the present embodiment, one such recessed portion is formed on each side of the central axis line L3. In other words, as shown in FIG. 4, the thick portion 50 of the present embodiment is shaped as an ellipse that is overall constricted in the central region in the lengthwise direction, that is to say the central region in the direction of the central axis line L3. This constriction is defined by a smooth curved line, and the thick portion 50 has a peanut shape overall. Also, the thick portion 50 of the present embodiment has a shape that is approximately line symmetrical with respect to the central axis line L3. Accordingly, the recessed portions 51a and 51b are arranged at positions that oppose each other across the central axis line L3.

Hereinafter, the two intersections where the boundary line L4 between the thick portion 50 and the peripheral portion 60 intersects the central axis line L3 will be referred to as points P1 and P2. The point P1 is the point more toward the toe side (first intersection), and the point P2 is the point more toward the heel side (second intersection). Also, the straight line that passes through the point P1 and is orthogonal to the central axis line L3 will be referred to as a straight line L5 (first orthogonal line), and the straight line that passes through the point P2 and is orthogonal to the central axis line L3 will be referred to as a straight line L6 (second orthogonal line). Furthermore, the intersection between the straight line L5 and the top line L1 will be referred to as a point P3, and the intersection between the straight line L6 and the top line L1 will be referred to as a point P4. Moreover, the intersection between the straight line L5 and the sole line L2 will be referred to as a point P5, and the intersection between the straight line L6 and the sole line L2 will be referred to as a point P6. Also, the straight line that passes through the face center Fc and is orthogonal to the central axis line L3 will be referred to as a straight line L7.

In general, hit points on the face surface are likely to be distributed along a straight line that is inclined from the heel side toward the toe side along the direction from the sole side to the top side and. Accordingly, the aforementioned straight line L7 is a hit point distribution line along which hit points are approximately distributed. In other words, when a golfer swings a golf club that includes the head 100, the points of impact between the ball and the face surface (hit points) will be distributed in the vicinity of the straight line L7. Also, the region surrounded by the top line L1, the sole line L2, and the straight lines L5 and L6 is a hit point distribution region A1 in which the hit points are approximately distributed. The hit point distribution region A1 has an approximately quadrangular shape with the above-described points P3 to P6 serving as the four corner points, and in the present embodiment, this region is approximately shaped as a parallelogram.

As described above, the hit point distribution region A1 has the thick portion 50 in the central region in the up-down direction. Accordingly, the face center Fc region is thick, thus ensuring strength for the head 100 with respect to impact during ball hitting. Also, the hit point distribution line L7 is orthogonal to the central axis line L3 of the thick portion 50 and extends so as to pass through the thick portion 50 via the central portion of the thick portion 50, and the recessed portions 51a and 51b are located on the hit point distribution line L7. Accordingly, the thick portion 50 does not occupy a large region along the direction of the hit point distribution line L7, and the relatively thinner transition portion 61 and thin portions 62a and 62b mainly occupy a large region along the direction of the hit point distribution line L7. As a result, the thin high restitution area spreads out along the actual hit point distribution, the interior of the hit point distribution region A1 flexes easily, and it is possible to improve the flight-distance. Note that although the straight line L7 is described above as being a hit point distribution line along which hit points are approximately distributed, there is no need for the regression line of a large number of actual hit points (referred to hereinafter as the “actual hit point distribution line”) and the straight line L7 to match. The actual hit point distribution line extends as indicated by L8 in FIG. 4, and is not necessarily orthogonal to the central axis line L3. However, even in such a case, if the actual hit point distribution line L8 intersects the central axis line L3, the actual hit point distribution line L8 will be approximately contained inside the hit point distribution region A1 that serves as the high restitution area, and the flight-distance is improved. Note that FIG. 8 shows an actual hit point distribution region A2 in which hit points are distributed when an average golfer makes actual hits. The actual hit point distribution region A2 is a region whose central axis is the actual hit point distribution line L8. As can be understood from this figure, the majority of the aforementioned hit point distribution region A1 is overlapped with the actual hit point distribution region A2.

Meanwhile, the transition portion 61 completely surrounds the thick portion 50, and has an approximately uniform width along the circumferential direction. Also, the transition portion 61 reaches the top line L1 and the sole line L2, and intersects the top line L1 and the sole line L2 in a line having a length, not in a point. Accordingly, the transition portion 61 extends over the entire face portion 11 in the top-sole direction, but is concentrated relatively in the central portion of the face portion 11 in the toe-heel direction, and reaches neither the heel-side end point Ph nor the toe-side end point Pt. Note that in the present embodiment, the centroid (geometrical center) of the region made up of the transition portion 61 and the thick portion 50 also approximately matches the face center Pc.

If the thickness of the face portion 11 rapidly decreased in the vicinity of the boundary line between the face portion 11 and the rising portion 12, stress would become concentrated in this thin portion, and there would be a risk of having an effect on the durability of the face portion 11. However, in the present embodiment, the transition portion 61 is continuous with the top line L1 and the sole line L2 as described above. In other words, the thick portion 50 does not suddenly end in the vicinity of the rising portion 12, nor does the thickness of the face portion 11 rapidly decrease. The strength of the face member 1 is therefore ensured.

Also, as shown in FIG. 4, a V-shaped slit (toe-side groove) 71 that has the toe-side end point Pt as its crest and extends along the boundary line between the face portion 11 and the rising portion 12 is formed on the inner surface (back surface) of the face portion 11. Similarly, a V-shaped slit (heel-side groove) 72 that has the heel-side end point Ph as its crest and extends along the boundary line between the face portion 11 and the rising portion 12 is formed on the heel side as well. In other words, regions thinner than the thin portions 62a and 62b are formed in the vicinity of the toe-side end point Pt and the heel-side end point Ph. Accordingly, due to these slits 71 and 72, the restitution factor can be raised particularly in the toe-side and heel-side portions, and it is possible to prevent the high restitution area from being biased toward the central region on the face surface, and to expand the high restitution area. As a result, it is possible to increase the flight-distance even if the ball is not grabbed at the central region of the face surface in a mishit or an intentional shot, for example.

In the present embodiment, a thickness w3 of the face portion 11 in the slit 71 is approximately constant, and the relationship w3<w2 is satisfied. Preferably, w3 can be set to 1.0 mm≦w3≦3.0 mm, or more preferably 1.5 mm≦w3≦2.5 mm, and in the present embodiment, w3=1.70 mm. Similarly, in the present embodiment, a thickness w4 of the face portion 11 in the slit 72 is approximately constant, and the relationship w4<w2 is satisfied. Preferably, w4 can be set to 1.0 mm≦w4≦3.0 mm, or more preferably 1.5 mm≦w4≦2.5 mm, and in the present embodiment, w4=w3=1.70 mm.

As shown in FIG. 4, the slits 71 and 72 are partially overlapped with the hit point distribution region A1. The slit 71 on the toe side begins at the toe-side end point Pt, extends along the top line L1 and arrives at the corner point P3, and then furthermore extends into the hit point distribution region A1 along the top line L1, but does not reach the corner point P4. Also, the slit 71 begins at the toe-side end point Pt and extends along the sole line L2, but does not reach the corner point P5. Similarly, the slit 72 on the heel side begins at the heel-side end point Ph, extends along the sole line L2 and arrives at the corner point P6, and then furthermore extends into the hit point distribution region A1 along the sole line L2, but does not reach the corner point P5. Also, the slit 72 begins at the heel-side end point Ph and extends along the top line L1, but does not reach the corner point P4.

As described above, in the present embodiment, the slits 71 and 72 extend inside the hit point distribution region A1. Accordingly, the interior of the hit point distribution region A1 can flex more easily, and it is possible to improve the flight-distance.

2. Second Embodiment

Next, a golf club head according to a second embodiment of the present invention will be described below with reference to FIG. 5. The head of the present embodiment is a utility golf club head, not a driver golf club head, and has a volume smaller than 400 cubic centimeters. FIG. 5 is a front view of a face portion 111 of the head of the present embodiment in the reference state. Note that it would not actually be possible to see the thickness structure formed on the inner surface of the face portion 111 in FIG. 5, but similarly to the case of FIG. 4, the thickness structure is illustrated in consideration of facilitating understanding.

As can be understood from comparing FIGS. 4 and 5, the head of the present embodiment has approximately the same configuration as the head 100 of the first embodiment, with mainly the exception that a later-described slit 73 is formed instead of the slits 71 and 72. For this reason, the following description focuses on differences from the first embodiment, and similar configurations will be denoted by the same reference signs and will not be described.

As shown in FIG. 5, the slit (groove) 73 is formed so as to extend along the sole line L2 at a position somewhat biased toward the heel side in the inner surface (back surface) of the face portion 111 of the present embodiment. In other words, a region thinner than the thin portions 62a and 62b is formed so as to extend along the sole line L2 at a position somewhat biased toward the heel side. This slit 73 contributes to an improvement in the restitution factor on the heel-side lower portion in particular. Specifically, it is possible to prevent the high restitution area from being biased toward the central region on the face surface, and to expand the high restitution area toward the heel-side lower portion. As a result, it is possible to increase the flight-distance even if the ball collides with the heel-side lower portion of the face surface in a mishit or an intentional shot, for example. Note that slits are not provided at positions along the top line L1 in the present embodiment. However, unlike the case of a driver, with a utility there is generally a tendency for the ball hit point to be comparatively biased toward the lower portion of the face surface. Accordingly, the flight-distance can be effectively extended with merely a slit extending along the sole line L2.

In the present embodiment, a thickness w5 of the face portion 111 in the slit 73 is approximately constant, and can be preferably set to 0.8 mm≦w5≦2.0 mm, or more preferably 1.0 mm≦w5≦1.5 mm. Also, in the present embodiment as well, the thickness w1 of the thick portion 50 is approximately constant, and can be preferably set to 1.5 mm≦w1≦2.5 mm, or more preferably 1.7 mm≦w1≦2.2 mm. Also, the thickness w2 of the thin portions 62a and 62b is also approximately constant and can be preferably set to 1.0 mm≦w2≦2.2 mm, or more preferably 1.4 mm≦w2≦2.0 mm.

The slit 73 is partially overlapped with the hit point distribution region A1. More specifically, the slit 73 extends so as to pass through the entirety of the hit point distribution region A1 along the sole line L2. The slit 73 extends beyond the corner point P5 toward the toe-side end point Pt, but does not reach the toe-side end point Pt, and similarly extends beyond the corner point P6 toward the heel-side end point Ph, but does not reach the heel-side end point Ph. As described above, the slit 73 extends inside the hit point distribution region A1, and therefore the interior of the hit point distribution region A1 can flex more easily, and it is possible to improve the flight-distance.

3. Variations

Although several embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the invention. The following are examples of modifications that can be made. The spirits of the following variations can be combined as appropriate.

3-1

Although the golf club head is a driver or utility type of golf club head in the above embodiments, there is no limitation to these types, and it may be a so-called fairway, hybrid, or iron type of golf club head, for example. It should be noted that the thickness distribution structure of the face portion of the present invention can be favorably applied to a wood type of golf club head.

3-2

Although the central axis line L3 is inclined relative to the top-sole direction in the above embodiments, it may extend parallel to the top-sole direction. In other words, the thick portion 50 may extend along the top-sole direction.

3-3

The shape of the thick portion 50 is not limited to the shapes described above. For example, as shown in FIG. 6, it may have a shape in which the recessed portions 51a and 51b are defined by an outline that has sharp corners rather than smooth curves.

Also, as shown in FIG. 7, either the recessed portion 51a or 51b can be omitted. In other words, the recessed portion may be formed on only one side of the central axis line.

3-4

In the first embodiment, either the slit 71 or 72 can be omitted. Also, in the second embodiment, a slit may be formed along the top line L1 in addition to the slit 73.

3-5

The face member 1 does not need to have a cup face structure, and the rising portion 12 can be omitted.

REFERENCE SIGNS LIST

1 Face member

11 Face portion

50 Thick portion

51a, 51b Recessed portion

60 Peripheral portion

61 Transition portion

62a, 62b Thin portion

71-73 Slit (groove)

100, 101 Golf club head

A1 Hit point distribution region

Fc Face center

L1 Top line

L2 Sole line

L3 Central axis line

L4 First orthogonal line

L5 Second orthogonal line

P1 First intersection

P2 Second intersection

P3 First corner point

P4 Second corner point

P5 Third corner point

P6 Fourth corner point

Pt Toe-side end point

Ph Heel-side end point

Claims

1. A golf club head comprising a face portion for hitting a ball,

wherein the face portion has a thick portion that includes a face center, and a peripheral portion that is thinner than the thick portion and surrounds the thick portion,

the thick portion extends along a central axis line that extends in a top-sole direction or in a direction inclined from a toe side toward a heel side along a direction from a sole side toward a top side, and

the thick portion has a recessed portion on at least one side of the central axis line so that a central region of the thick portion along the central axis line is recessed more toward the central axis line than parts of the thick portion on two sides of the central region along the central axis line.

2. The golf club head according to claim 1, wherein the thick portion has the recessed portion on each side of the central axis line.

3. The golf club head according to claim 2, wherein the recessed portions on both sides of the central axis line oppose each other across the central axis line.

4. The golf club head according to claim 1,

wherein the central axis line is a line segment having a maximum length among line segments that pass through a centroid of the thick portion and are overlapped with the thick portion, and intersects a boundary line of the thick portion at a first intersection and a second intersection,

the face portion includes a hit point distribution region, and the hit point distribution region is surrounded by a first orthogonal line that passes through the first intersection and is orthogonal to the central axis line, a second orthogonal line that passes through the second intersection and is orthogonal to the central axis line, and a boundary line of the face portion, and

a groove that extends along the boundary line of the face portion and is at least partially overlapped with the hit point distribution region is formed on a back surface side of the face portion.

5. The golf club head according to claim 4,

wherein the boundary line of the face portion includes a top line on a top side that extends between a toe-side end point, being a point farthest on a toe side, and a heel-side end point, being a point farthest on a heel side, and includes a sole line on a sole side that extends between the toe-side end point and the heel-side end point,

the hit point distribution region has a first corner point on a toe side and a second corner point on a heel side on the top line, and has a third corner point on a toe side and a fourth corner point on a heel side on the sole line, and

the groove includes at least one of a toe-side groove and a heel-side groove, the toe-side groove extends at least from the first corner point into the hit point distribution region along the boundary line of the face portion but does not reach the second corner point, and the heel-side groove extends at least from the fourth corner point into the hit point distribution region along the boundary line of the face portion but does not reach the third corner point.

6. The golf club head according to claim 5, wherein the groove includes both the toe-side groove and the heel-side groove.

7. The golf club head according to claim 5, having a volume of 400 cubic centimeters or more.

8. The golf club head according to claim 6, having a volume of 400 cubic centimeters or more.

9. The golf club head according to claim 4,

wherein the boundary line of the face portion includes a sole line on a sole side that extends between a toe-side end point, being a point farthest on a toe side, and a heel-side end point, being a point farthest on a heel side, and

the groove extends along the sole line.

10. The golf club head according to claim 9, having a volume less than 400 cubic centimeters.

11. A golf club head comprising a face portion for hitting a ball,

wherein the face portion has a thick portion that includes a face center and has an approximately uniform thickness, and a peripheral portion that is thinner than the thick portion and surrounds the thick portion,

the thick portion extends along a central axis line that extends in a direction from toe-down to heel-up,

the central axis line is a line segment having a maximum length among line segments that pass through a centroid of the thick portion and are overlapped with the thick portion, and

the thick portion has a recessed portion on at least one side of the central axis line so that a central region of the thick portion along the central axis line is recessed more toward the central axis line than parts of the thick portion on two sides of the central region along the central axis line, thus approximately forming a shape as obtained by providing an ellipse whose long axis extends substantially along the central axis line with the recessed portion.

12. The golf club head according to claim 11, wherein the thick portion does not reach the boundary line of the face portion on both the top side and the sole side.

13. The golf club head according to claim 11, wherein an angle θ1 formed by the central axis line and a horizontal direction satisfies a condition θ1<60°.

14. The golf club head according to claim 12, wherein an angle θ1 formed by the central axis line and a horizontal direction satisfies a condition θ1<60°.

15. The golf club head according to claim 11, wherein the ellipse has a shape that is approximately line symmetrical with respect to the central axis line.

16. The golf club head according to claim 12, wherein the ellipse has a shape that is approximately line symmetrical with respect to the central axis line.

17. The golf club head according to claim 13, wherein the ellipse has a shape that is approximately line symmetrical with respect to the central axis line.

18. The golf club head according to claim 14, wherein the ellipse has a shape that is approximately line symmetrical with respect to the central axis line.

19. A golf club head comprising a face portion for hitting a ball,

wherein the face portion has a thick portion that includes a face center and has an approximately uniform thickness, and a peripheral portion that is thinner than the thick portion and surrounds the thick portion,

the thick portion extends along a central axis line that extends in a top-sole direction that is a vertical direction,

the central axis line is a line segment having a maximum length among line segments that pass through a centroid of the thick portion and are overlapped with the thick portion, and

the thick portion has a recessed portion on at least one side of the central axis line so that a central region of the thick portion along the central axis line is recessed more toward the central axis line than parts of the thick portion on two sides of the central region along the central axis line, thus approximately forming a shape as obtained by providing an ellipse whose long axis extends substantially along the central axis line with the recessed portion.