Golf club

Abstract

A golf club enables a golf ball to be hit farther without a decrease in ball traveling distance even if it is struck at a lower point on the club head face. A driver club head includes a face having a hitting surface, a sole forming the bottom of the head, etc. The sole is modified for improvement by providing an elastically deformable area having a recessed or projected configuration at a position of the sole closer to the face. The deformable area includes a bent portion formed at the lower end of the face. A bend is formed between the bent portion and the sole at an obtuse angle. The sole is provided with a recess or a projection to lower the rigidity of the sole. Thus, repulsion is enhanced to increase the ball traveling distance even if the ball is struck at a lower point on the face.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to golf clubs. More particularly, the present invention relates to an improved golf club having a club head sole modified to increase the traveling distance of golf balls.

[0003] 2. Description of the Related Art

[0004] There are various golf clubs prepared for varying conditions of golf courses. For the first shot, golf clubs called “drivers” are usually used in order to get maximum ball traveling distance. The ball traveling distance affects the score directly. Therefore, the position of the ball impact point on the golf club head is an important factor. The hitting surface of the club head is called “face”. Under any conditions, the user (player) will strike the ball on the face of the club head.

[0005] Usually, the center of gravity of a driver club head as projected on the club face is located above the center of the face as seen from a direction perpendicular to the face surface. The reason for this is as follows. The club head has an approximately inverted trapezoidal or triangular configuration in terms of the face configuration, in which the upper side is wider than the lower side. Accordingly, the mass is inevitably deviated toward the upper side. In addition, because a part known as “hosel”, into which a shaft is to be inserted, is provided on the top of the club head, an extra mass is added to the upper side of the head.

[0006] Regarding the center of gravity, even a club head in which the center of gravity is located at a position approximately 60% from the bottom surface of the head in terms of the face height, for example, is called “low-center of gravity model”. A ball striking area called “sweet area” is in the vicinity of the center of gravity, which is an area capable of sending the ball the farthest distance. Therefore, in order to make use of the maximum repulsion power of the head to maximize the ball traveling distance, it is usually necessary to strike the ball on a sweet area above the center of the face. However, not only amateur golfers whose ball impact point is likely to vary but also professional golfers occasionally shift their ball impact point intentionally according to golf course conditions.

[0007] For example, in a head (against) wind, golfers usually hit the ball in such a manner as to produce a low ball trajectory because if it is hit in the usual manner, the ball will have to fly against the wind, resulting in a failure to get the desired ball traveling distance. In this case, the ball impact point is in a lower area of the club face. This, however, results in degradation of the repulsive force obtained. Consequently, the ball traveling distance achievable becomes less than that obtained by striking on the sweet area. This is because the center of gravity is located at the upper side of the face, as stated above. That is, because the sweet area, which is a high-repulsion area, is in the vicinity of the center of gravity, if the impact point is off this area, repulsive force reduces undesirably.

[0008] Under these circumstances, various methods have been proposed to enable a repulsive force comparable to that obtained at the conventional sweet area to be obtained even at a lower point on the face to thereby solve the problems associated with the conventional golf clubs. For example, a golf club has been disclosed in which the area of a region of the club face that has a specific coefficient of restitution is specified to minimize the decrease in ball traveling distance when the ball impact point is offset from the sweet spot, as a method of increasing repulsive force [for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-17912]. As a method of lowering the center of gravity and consequently increasing repulsive force at a lower point on the club face, a technique has been disclosed wherein a weight member that is wider at the lower side than the upper side thereof is provided in a lower portion of the club head [for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-17908]. Further, there is known a golf club having a head arranged to allow its face to be deflected with good balance [for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 11-114102].

[0009] As has been stated above, various methods have been devised to increase the ball traveling distance under various conditions. However, the proposed methods have not yet satisfactorily solved the problems. There is still room for further improvement, particularly in terms of enhancement of repulsion at a lower point off the sweet area. The above-described method wherein the area of a region of the club face that has a specific coefficient of restitution is specified is specifically carried out by reducing the thickness of a specific region of the face so that the thickness varies from the center to the peripheral edge of the face, thereby consequently enhancing the repulsion effect.

[0010] The above-described face structure may be effective for specific club heads but is not always reliable. The structure in which the club face, including the crown, is deflectable with good balance is also incapable of surely enhancing the repulsion effect at a lower point on the face. The method wherein a weight member is provided is effective in its own way but limited in its usefulness under the recent tendency for club heads to increase in size. That is, when a club head becomes large in size, addition of a weight member gives rise to a new problem that the mass of the head becomes heavy. The golf industry is a world where tradition is valued originally.

[0011] Substantial changes in the configuration, weight, etc. of the club head from those of the conventional one require users to change their golf swing and so forth. This may cause the swing rhythm to be destroyed. Even if an epoch-making golf club is developed, it will take a long time for the new golf club to become established in actual practice. Thus, various problems will occur if large-scale changes are made to the configuration of golf clubs that have actually been established. Therefore, it is ideal to develop a golf club improved in function to satisfy golfers without substantial change in the configuration of the presently established golf clubs.

[0012] Accordingly, it is desired to develop a golf club capable of enlarging the repulsion area, particularly, downward on the club head face, without making a large difference from the conventional configuration and without requiring a special arrangement that limits the functions of the golf club, whereby the repulsion performance is improved even at a lower point on the club head face as well as in the conventional sweet area, and thus the ball traveling distance can be increased stably even under headwind conditions.

SUMMARY OF THE INVENTION

[0013] The present invention was made in view of the above-described technical background. Accordingly, the present invention attains the following objects.

[0014] An object of the present invention is to provide a golf club improved to increase repulsive force at a lower point on the club head face so that the ball can be hit farther without a decrease in ball traveling distance even if it is struck at a point below the conventional sweet area.

[0015] Another object of the present invention is to provide a golf club improved in ball hitting performance in comparison to the conventional golf clubs, despite having the same basic configuration as the conventional one, simply by modifying a part of the club head sole, without a change from the conventional structure in terms of the configuration as seen from the player upon addressing.

[0016] Still another object of the present invention is to provide a golf club capable of being produced at reduced costs.

[0017] To attain the above-described objects, the present invention provides the following golf clubs.

[0018] According to a first aspect thereof, the present invention provides a golf club having a metallic hollow golf club head. The golf club includes a face member disposed at the front of the club head and having a hitting surface for hitting a golf ball. The golf club further includes a head body member constituting the remaining part of the club head. The head body member has a sole forming the bottom of the club head, a crown forming the top of the club head, a toe forming the forepart of the club head, a heel forming the rear part of the club head, a back positioned opposite the face member to form the back part of the club head, and a hosel to which a club shaft is connected. A deformable area that is elastically deformable in response to hitting of the golf ball on the hitting surface is provided at the joint between the lower end of the face member and the sole.

[0019] A golf club according to a second aspect of the present invention is a golf club of the first aspect, wherein the deformable area includes a lower end portion of the face member that is bent at an angle not less than 90 degrees to form a bent portion, and the sole is joined to the bent portion. The sole is convexly projected toward the top of the club head in a section taken along a vertical plane containing a line perpendicular to the hitting surface.

[0020] A golf club according to a third aspect of the present invention is a golf club of the first aspect, wherein the deformable area includes a lower end portion of the face member that is bent at an angle not less than 90 degrees to form a bent portion, and the sole is jointed to the bent portion. The sole is convexly projected away from the top of the club head in a section taken along a vertical plane containing a line perpendicular to the hitting surface.

[0021] A golf club according to a fourth aspect of the present invention is a golf club of the first aspect, wherein the deformable area includes a lower end portion of the face member that is bent at an angle not less than 90 degrees to form a bent portion, and the sole is joined to the bent portion. The sole is provided with at least one hole.

[0022] A golf club according to a fifth aspect of the present invention is a golf club of the first aspect, wherein the deformable area includes a lower end portion of the face member that is bent at an angle not less than 90 degrees to form a bent portion, and the sole is joined to the bent portion. The sole has a part thereof replaced with a thin plate.

[0023] A golf club according to a sixth aspect of the present invention is a golf club of the first aspect, wherein the deformable area includes a lower end portion of the face member that is bent at an angle not less than 90 degrees to form a bent portion, and the sole is joined to the bent portion. The sole is divided into two portions at a part thereof. The two portions are displaceable relative to each other.

[0024] A golf club according to a seventh aspect of the present invention is a golf club of the second or third aspect, wherein the sole in the deformable area has a smaller plate thickness than that of the bent portion.

[0025] A golf club according to an eighth aspect of the present invention is a golf club of the second aspect, wherein a part of the sole in the deformable area forms an arch-shaped groove.

[0026] A golf club according to a ninth aspect of the present invention is a golf club of the second aspect, wherein a portion of the sole that is joined to the bent portion in the deformable area forms a groove having a surface approximately parallel to the hitting surface.

[0027] A golf club according to a tenth aspect of the present invention is a golf club of the seventh aspect, wherein the deformable area has a gentle bend G formed by intersection of a line S1 tangent to the surface of the face member with a line S2 tangent to the bent portion of the face member. The bend G has an angle &agr; not less than 90 degrees. The deformable area further has a gentle bend H formed by intersection of the tangent line S2 with a line S3 tangent to the surface of the sole. The bend H has an angle &agr;1 not less than 90 degrees.

[0028] A golf club according to an eleventh aspect of the present invention is a golf club of the tenth aspect, wherein the deformable area has at least one arch-shaped groove provided in a surface of the sole near the bend H. A gentle bend J is formed by intersection of a line S4 tangent to the groove with the tangent line S2. The bend J has an angle &agr;2 not less than 90 degrees. Further, a gentle bend K is formed by intersection of a line S5 tangent to the groove with the tangent line S3. The bend K has an angle &agr;3 not less than 90 degrees. The bends G, J and K form a continuous gently curved line.

[0029] A golf club according to a twelfth aspect of the present invention is a golf club of the tenth or eleventh aspect, wherein the angle &agr; of the bend G is not less than 90 degrees and not more than 135 degrees, preferably not less than 90 degrees and not more than 120 degrees.

[0030] The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is an external view showing the appearance of a golf club.

[0032] FIG. 2 is a plan view of a driver club head according to the present invention.

[0033] FIG. 3 is a front view of the driver club head according to the present invention.

[0034] FIG. 4 is a side view of the driver club head according to the present invention, which shows a first embodiment of the present invention.

[0035] FIG. 5 is a side view of a conventional driver club head.

[0036] FIG. 6 is a sectional view taken along the line X-X in FIG. 3.

[0037] FIG. 7 is a sectional view showing the details of the structure shown in FIG. 6.

[0038] FIG. 8 is an explanatory view illustrating a state where a golf ball has been struck on the face of the club head.

[0039] FIG. 9 is a sectional view showing a third embodiment of the present invention.

[0040] FIG. 10 is a sectional view showing a fourth embodiment of the present invention.

[0041] FIG. 11 is a sectional view showing a fifth embodiment of the present invention.

[0042] FIG. 12 is a sectional view showing a sixth embodiment of the present invention.

[0043] FIG. 13 is a sectional view showing a seventh embodiment of the present invention.

[0044] FIG. 14 is a sectional view showing an eighth embodiment of the present invention, in which the club head has a groove with a rectangular sectional configuration.

[0045] FIG. 15 is a sectional view showing a ninth embodiment, in which the club head has a groove with a stepped sectional configuration.

[0046] FIG. 16 is a sectional view showing a modification in which a part of the sole of the club head is made of a thin plate to lower the rigidity of the sole.

[0047] FIG. 17 is a sectional view showing a modification in which the sole of the club head is divided into two portions to lower the rigidity of the sole.

[0048] FIG. 18 is a sectional view showing a modification in which the sole of the club head is provided with at least one hole to lower the rigidity of the sole 3.

[0049] FIG. 19 is a diagram showing the distribution of coefficients of restitution in the club head according to the first embodiment.

[0050] FIG. 20 is a diagram showing the distribution of coefficients of restitution in a conventional club head.

[0051] FIG. 21 is an explanatory view showing a measurement comparison as to ball traveling distance between the first embodiment and the conventional golf club.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0053] FIG. 1 is an external view showing the general structure of a golf club according to the present invention. Although the present invention is directed to a metallic hollow golf club head, the following description of embodiments will be made of an example in which the present invention is applied to a driver club head. A driver club head (hereinafter referred to simply as “head”) 1 is supported on a shaft A. FIGS. 2 to 4 show an embodiment of the head 1 as used in a metallic golf club. It should be noted that the drawings other than FIG. 1 show only the head part. That is, illustration of the shaft A and other members is omitted therein.

[0054] FIG. 2 is a plan view. FIG. 3 is a front view, and FIG. 4 is a side view. As shown in the figures, the head 1 comprises a crown 2 corresponding to the top of the head 1, a sole 3 corresponding to the bottom of the head 1, a face 4 with which a golf ball is struck, a toe 5 corresponding to the forepart of the head 1, a heel 6 corresponding to the rear part of the head 1, a back 12 positioned opposite the face 4 to form the back part of the head 1, and a hosel 7, which is a member for supporting the head 1 on the shaft A.

[0055] In the manufacture of the head 1, each part comprises either a single unitized member or a plurality of equally divided members that are joined together to form one component part. Each component part is subjected to press working before being joined together into an integrated structure by welding or the like. For example, the head 1 comprises five component parts, i.e. a face 4, a sole 3, a crown 2, a hosel 7, and a weight. Each part is produced as follows. A plate material is blanked into a predetermined shape. The blank is formed under heating by hot pressing. The heating process is performed, for example, at 400° C. for the face 4, and at 900° C. for the sole 3, the crown 2 and other portions of the head body.

[0056] After being pressed, each component part is deburred (trimmed) and joined together by TIG arc welding to produce a driver club head 1. In this embodiment, the constituent material of the head 1 is a titanium alloy. The component parts are joined together as follows. The constituent members related to the face 4 and those related to the sole 3 are butt-joined to each other. Thereafter, the hosel-related members are joined thereto, and the pressed crown-related members are joined by TIG arc welding. In this way, the component parts are integrated into a driver club head 1. After the welding process, the driver club head is subjected to grinding process and age hardening (5 hours at 515° C.), followed by painting process. Thus, the driver club head is completed.

[0057] The face 4 has a slightly curved surface and is formed from a plate-shaped material. In the face 4, a sweet area 9 in the vicinity of the center 8 of gravity has the maximum coefficient of restitution. Usually, an effective way of sending a golf ball a long distance is to hit the ball at the sweet area 9. Therefore, the coefficient of restitution is set high in this portion of the face 4. It is well known that as the coefficient of restitution is increased, the ball traveling distance increases. The coefficient of restitution is an important factor determining the performance of golf clubs. For the coefficient of restitution, a criterion of measurement has been defined by the United States Golf Association (USGA). The coefficient of restitution is obtained from the following equation:

Vout/Vin=eM−m/M+m

[0058] In the above equation, m represents the average mass of balls for testing, M represents the mass of the head, Vout represents the speed of a testing ball after impact, and Vin represents the speed of the testing ball before impact. Accordingly, Vout/Vin shows the speed ratio. Further, e represents the coefficient of restitution. According to the definition, golf balls for testing should be Pinnacle Gold (trade name) golf balls, and testing balls that have previously been numbered and measured for initial velocity should be used. The average weight should be 45.4 g.

[0059] It is defined that the testing balls should be stored in a room at 23±1.0° C., and the impact speed should be 48.8 m/s. In addition, a ball launching apparatus, a trajectory screen and other testing equipment have been specified in detail. Regarding a testing method also, rules have been made in detail. For example, mapping should be performed. A reference value of the coefficient of restitution is e=0.822. Whether each particular head is conformable or not is judged by comparing the actual impact speed ratio with the reference speed ratio on the basis of the measured mass according to the above-described definition.

[0060] Meanwhile, the coefficient of restitution can be calculated inversely from the above-described equation, provided that the other conditions are determined. In other words, the coefficient of restitution is calculated for various values of the mass of the head that may be changed, for example, by varying the thickness of the face 4. In this way, it is possible to judge optimal numerical value setting. As will be clear from the above-described equation, the fact that the speed of a golf ball after impact is high means that the coefficient of restitution is high.

[0061] The present inventor conducted exhaustive studies by performing testing according to the above-described rules and attained the present invention in which the conventional sweet area is extended downward and thus widened.

[0062] Embodiments of the present invention will be described below in detail. FIG. 5 is a side view of a conventional driver club head, which corresponds to a side view of the first embodiment of the present invention shown in FIG. 4. As will be understood from comparison with FIG. 5, the present invention has an improvement made on the sole 3. As shown in FIG. 4, a portion of the sole 3 closer to the face 4 is provided with a projection 10 and a groove 11 that extend in a direction connecting the toe 5 and the heel 6. The projection 10 projects away from the crown 2, and the groove 11 is recessed toward the crown 2. The projection 10 comprises a first projection 10a and a second projection 10b facing each other across the groove 11. The first projection 10a is located closer to the face 4. The second projection 10b is formed as a gentle projection extending toward the heel 6, which is the rear part of the head 1.

[0063] As shown in FIG. 4, the projection 10 and the groove 11 have a gently curved configuration as a whole. The face-side projection 10a makes the sole 3 form an obtuse angle &agr; to the face 4 (see FIG. 6) in a section taken along a vertical plane (plane containing a straight line in a direction shown by a thread suspending an object) containing a line perpendicular to the surface of the face 4. The purpose of providing a recessed and projected area on the sole 3 is to impart an elastic effect to the sole 3. The recessed and projected area as an elastically deformable area B is a constituent part featuring this embodiment. FIG. 6 is a sectional view taken along the line X-X in FIG. 3, schematically showing the first embodiment.

[0064] The head 1 is a component formed by press working, as has been stated above. Accordingly, a portion of the head 1 corresponding to the external line of the head structure shown in FIG. 6 is defined by pressed members formed of a titanium alloy. The interior C is a hollow space. In FIG. 6, line D shows the position of the sole of the conventional club head. In contrast thereto, this embodiment has a structure in which the sole 3 partly projects and has the deformable area B at a position closer to the face 4, as shown in FIG. 6. The projecting height E of the deformable area B is of the order of 6 mm in this embodiment. When impact force F is applied to the surface of the face 4 in the direction of the arrow shown in FIG. 6, the head itself is elastically deformed complicatedly. In this embodiment, the elastic deformation is made concentrated toward the sole 3 as much as possible by providing the recessed and projected deformable area B on the sole 3.

[0065] As a result, the sole 3 has a considerable elastic effect even if the face 4 is left unchanged from the conventional configuration and even if compared to a conventional structure in which the thickness of the lower portion of the face 4 is reduced to increase repulsive force, for example. Thus, it is possible to avoid the problem that the rigidity of the head is undesirably weakened by excessively reducing the thickness of the face 4 with the intention of increasing repulsive force. The deformable area B is not necessarily limited to the configuration shown in this embodiment. The deformable area B may have any configuration that produces an elastic effect. However, it is preferable for the deformable area B to have a recessed and/or projected configuration.

[0066] FIG. 6 is a schematic view of the X-X section of FIG. 3, whereas FIG. 7 is a detailed view of the X-X section. Next, the structure of the deformable area B will be described in detail with reference to FIG. 7. As has been stated above, the face 4 is bent at a lower portion thereof toward the sole 3 to form a bent portion 4a. The curving part between the face 4 and the bent portion 4a constitutes a first bend G.

[0067] The first bend G means a part formed by intersection of a line S1 tangent to the face 4 approximately at the center thereof with a line S2 tangent to the bent portion 4a approximately at the center thereof. The bend G is defined by a gently curved surface contiguous to the tangent lines S1 and S2 at the point of intersection thereof. The angle &agr; of the bend G is not less than 90 degrees and not more than 135 degrees. Preferably, the angle &agr; is not less than 90 degrees and not more than 120 degrees. This has been confirmed on the basis of measured data. The angle &agr; is measured by using a protractor. The surface of the face 4 is rounded approximately uniformly. Therefore, the measurement is carried out in such a manner that when the protractor is applied to the surface of the face 4, that is, when a tangent is drawn to the face surface, the gap between the straight line and the curved line is approximately the same at the left and right sides or at the upper and lower sides. The bent portion 4a as bent constitutes a part of the sole 3.

[0068] An end portion of the sole 3 is joined to the distal end of the bent portion 4a by welding. The plate thickness t2 of the sole 3 is smaller than the plate thickness t1 of the face 4. In the embodiment illustrated in the figures, an arch-shaped groove I (11) is provided in the sole 3. The groove I is defined by a gently curved line extending immediately from the end of the sole 3. The end of the arch-shaped groove I forms a continuous gently curved line and constitutes a third bend J in combination with the bent portion 4a. The third bend J is formed as a gentle bend by intersection of the tangent line S2 to the bent portion 4a approximately at the center-thereof with a line S4 tangent to approximately one rising portion of the groove I. The angle &agr;2 of the bend J is an obtuse angle not less than 90 degrees.

[0069] Further, the groove I constitutes a gently curved fourth bend K in combination with a portion of the sole 3 closer to the back 12. The fourth bend K is formed as a gentle bend by intersection of a line S5 tangent to approximately the other rising portion of the groove I with a line S3 tangent to the sole 3. The angle &agr;3 of the bend K is an obtuse angle not less than 90 degrees. Although the illustrated example has only one arch-shaped groove I, a plurality of arch-shaped grooves may be provided. Each of the bends G, J and K, including the groove I, constitutes a part of the deformable area B. With the above-described structure of the deformable area B, the face-side portion of the head 1 is kept highly rigid as in the conventional club head, and the rigidity of the sole-side portion of the head 1 is made lower than that of the face-side portion of the head 1.

[0070] It should be noted that the sectional configuration shown in FIG. 7 is provided with a single recess (as seen from the outside of the sole 3). In other words, the sectional configuration shown in FIG. 7 is as follows. Assuming that the angle (&agr;) of clockwise rotation from the tangent line S1 to the tangent line S2 is a plus angle and the angle (&agr;) of counterclockwise rotation is a minus angle, the rotation angle (&agr;) changes between plus and minus sequentially: the angle (&agr;) is plus in rotation from the tangent line S1 to the tangent line S2, plus in rotation from the tangent line S2 to the tangent line S4, minus in rotation from the tangent line S4 to the tangent line S5, and plus in rotation from the tangent line S5 to the tangent line S3. The fact that there are sequential plus rotations and one minus rotation from the tangent line S1 to the tangent line S3, that is, there is one rotation angle change between plus and minus, means that the sole 3 is formed with one recess. If there are two rotation angle changes between plus and minus, it means that the sole 3 is formed with two recesses. In the example shown in FIG. 7, the angle change between plus and minus is within 90 degrees. This means that the recess is a concave groove having a gentle curvature.

[0071] If there is no angle change from plus to minus, the sole 3 has no recess. In other words, the head structure may have, roughly speaking, a sectional configuration along a linear contour defined by the tangent lines S2 and S3 intersecting each other, in which the sole 3 has a second bend H formed from a projection, as shown in FIG. 7. The second bend H is formed as a gentle bend by intersection of the line S2 tangent to the bent portion 4a with the line S3 tangent to the surface of the sole 3 approximately at the center thereof. The angle &agr;1 of the second bend H is an obtuse angle not less than 90 degrees.

[0072] The crown 2 has the same structure as in the conventional club head. The face-side portion of the crown 2 looks unchanged from the conventional structure as seen from the player upon addressing. Because the sole-side portion of the head 1 is made lower in rigidity than the face-side portion of the head 1, the lower portion of the face 4 is easily deflectable upon hitting a golf ball. With the gently curved structure, the shock is lessened, and the likelihood of the head 1 being cracked at impact is eliminated. In addition, the spring effect is enhanced. Consequently, the conventional sweet area extends toward the sole 3. That is, the sweet area widens downward. Thus, the repulsion effect is enhanced.

[0073] If a golf ball is struck at a lower point on the face 4 (at a position below approximately 60% of the height of the face 4 from the sole 3), the lower portion of the surface of the face 4 is deflected by a spring effect produced by deflection of the sole 3 through the gently curved portion and the groove I, thereby enhancing the repulsion effect. As a result, the golf club according to this embodiment enables the conventional sweet area to extend downward on the surface of the face 4 and hence allows the sweet area to be widened. Accordingly, even if the player strikes a golf ball at a lower point on the face 4, there will be no decrease in ball traveling distance as occurs with the conventional golf clubs. Thus, the golf club according to this embodiment enables the player to stably get better distance. Further, because it has a widened sweet area, the head 1 of this embodiment is capable of increasing the maximum coefficient of restitution.

[0074] FIG. 8 is an explanatory view schematically showing a state where a ball has been struck on the hitting surface of the face 4. This is the state F shown in FIG. 6. The theoretical contents of the above-described structure of the embodiment will be explained below in detail with reference to FIG. 8. When a ball 23 is struck on the face 4, the face 4 is deformed toward the back 12 as shown by the chain double-dashed line in the figure. The ball 23 is also deformed. If the amount of deformation of the ball 23 is reduced, the hysteresis loss due to deformation of the ball 23 when it returns to the previous spherical shape by its own elasticity is reduced, and thus the impact energy loss of the ball 23 is minimized. If the amount of deformation of the face 4 is increased, the amount of deformation of the ball 23 can be reduced relatively. Consequently, it is possible to increase the coefficient of restitution and to hit the ball 23 a longer distance.

[0075] When the ball 23 is struck on the face 4, the sole 3 is also deformed downward in association with the deformation of the face 4. In the conventional club head, the angle formed between the face 4 and the sole 3 is an acute angle, as shown in FIG. 5. Therefore, the face 4 and the sole 3 are not sufficiently deformable. In this embodiment, however, the angle between the face 4 and the sole 3 is set not less than 90 degrees, as shown by G in FIG. 7. As a result, the face 4, particularly a region below the center of the surface of the face 4, is lower in rigidity than in the conventional club head and hence easily elastically deformable upon hitting the ball 23. Thus, the lower portion of the face 4 is elastically deformed to a considerable extent in comparison to the conventional club head by a synergistic effect of the face 4 and the sole 3. For this reason, when the ball 23 is struck on a lower portion of the hitting surface of the face 4, the ball 23 is sent a longer distance effectively without lowering the coefficient of restitution in comparison to the conventional club head.

[0076] FIG. 9 shows a second embodiment of the present invention. In this case, a portion of the sole 3 closer to the face 4 is formed with only a projection 13 projecting flat in comparison to the conventional club head on the assumption that the bend between the face 4 and the sole 3 is formed at an obtuse angle &agr; in a section taken along a vertical plane containing a line perpendicular to the surface of the face 4. In comparison to the arrangement of the foregoing embodiment, the club head according to this embodiment has no groove but a flat projection 13 between the back 12 and the face 4. When an impact is applied to the face 4, the projection 13 is elastically deformed to increase the coefficient of restitution of the club head.

[0077] FIG. 10 shows a third embodiment of the present invention, in which the whole sole 3 is curvedly projected outward as a projection 14 over from the face 4 to the back 12.

[0078] FIG. 11 shows a fourth embodiment of the present invention, in which the whole sole 3 is curvedly projected inward as a recess 15 over from the face 4 to the back 12.

[0079] FIG. 12 shows a fifth embodiment of the present invention, in which a part of the bent portion 4a closer to the joint with the sole 3 is bent approximately parallel to the face 4 to form a bent portion 16 having a turn-back surface. The sole 3 extending from the bent portion 16 to the back 12 is approximately flat and in a straight-line form in the sectional view of FIG. 12. When an impact is applied to the face 4, the bent portion 16 is deformed to a considerable extent.

[0080] FIG. 13 shows a sixth embodiment of the present invention. In this case, a portion of the sole 3 closer to the face 4 is formed with a plurality of recesses and projections on the assumption that the bend between the face 4 and the sole 3 is formed at an obtuse angle &agr; in a section taken along a vertical plane containing a line perpendicular to the surface of the face 4. As shown in the figure, three projections 17 and two grooves 18 are provided. The repulsion effect is the same as the above. However, the recessed and projected configuration is somewhat smaller in size than in the above-described example owing to the restriction on the space.

[0081] FIGS. 14 and 15 show seventh and eighth embodiments, respectively, of the present invention, in which the groove I (11) is modified. In FIG. 14, the club head has a groove 19 with a rectangular sectional configuration. In FIG. 15, the club head has a groove 20 with a stepped sectional configuration. Both the seventh and eighth embodiments provide the same advantageous effects as the above.

[0082] FIG. 16 shows a modification in which the club head is arranged to lower the rigidity of the sole 3. That is, a part of the sole 3 is made of a thin plate 21 to lower the rigidity of the sole 3.

[0083] FIG. 17 shows a modification in which the club head is arranged to lower the rigidity of the sole 3. The sole 3 is divided into two portions 3a and 3b so that when an impact is applied to the face 4, the divided portions 3a and 3b are slidable relative to each other.

[0084] FIG. 18 shows a modification in which the club head is arranged to lower the rigidity of the sole 3. A part of the sole 3 closer to the face 4 is provided with at least one hole 22 to lower the rigidity of the sole 3.

[0085] Although various embodiments have been described above, the present invention is not necessarily limited to the described embodiments. The deformable area B preferably has the above-described recessed and/or projected configuration. However, the deformable area B may have a gentle V-shaped configuration or a bellows-like configuration. The deformable area B may have any configuration, provided that it enhances the elastic effect and lowers the rigidity of the sole 3.

EXAMPLES

[0086] The following is a description of examples carried out to examine the improvement in performance with regard to the above-described club head structures. FIG. 19 shows the results of an experiment carried out on the golf club according to the first embodiment. FIG. 19 shows a distribution of coefficients of restitution measured when a golf ball was struck on the face 4. Based on the experimental results, points of the same coefficient of restitution were plotted as contour lines. FIG. 20 shows the results of an experiment carried out on a conventional golf club under the same conditions as in the case of FIG. 19. The experiments were performed under the following conditions: 1 Face material: cold rolled material of Ti-15V-3Cr-3Sn-3Al plate thickness: 2.9 mm Sole material: Ti-15V-3Cr-3Sn-3Al plate thickness: 1.15 mm Crown material: Ti-15V-3Cr-3Sn-3Al plate thickness: 1.0 mm Volume: about 300 cc mass: about 196 g.

[0087] It will be clear from comparison of FIG. 19 with FIG. 20 that high values of the coefficient of restitution are distributed closer to the sole side in FIG. 19. This means that even if a golf ball is struck at a point on the face surface closer to the sole, the ball can be hit a farther distance than with the conventional golf club.

[0088] FIG. 21 shows measurements of ball traveling distance obtained by a hitting test using a golf ball hitting robot to compare the embodiment of the present invention with a conventional golf club. FIG. 21 shows a measurement comparison at a head speed of 40 m/s. The height H of the point of measurement is the distance from the leading edge, as shown in FIG. 21. In FIG. 21, Example represents the first embodiment of the present invention, and Comparative Example represents a conventional golf club. The test was performed by using a golf ball hitting robot. Example and Comparative Example were carried out under the same hitting conditions. The hitting conditions are as shown in FIG. 21.

[0089] The specifications of the clubs used in the test are as follows: 2 Club length: 44.5 inches Balance: D2 Loft angle &bgr;: 10.5 degrees Lie angle &ggr;: 56.5 degrees Shaft FLEX: R

[0090] In comparison of the measurements of ball travelling distance, at a point of measurement at a height H of 18 mm, for example, the ball travelling distance of Example is 204 yards, whereas that of Comparative Example is 199 yards. It will be clear from the difference in the ball travelling distance that the structure of the present invention is advantageously effective.

[0091] As has been detailed above, the golf club according to the present invention is arranged such that the sole of the club head has an elastic effect. Accordingly, repulsive force obtained at a lower point on the face is increased. Therefore, even if a golf ball is struck at a point below the conventional sweet area, the ball can be hit a long distance without a decrease in ball traveling distance.

[0092] Further, the basic configuration of the club head is left unchanged from that of the conventional golf clubs, but only a part of the sole of the club head is modified. Therefore, the external appearance of the club head looks unchanged from the conventional structure as seen from the player upon addressing. Nevertheless, the golf club according to the present invention exhibits improved ball-hitting performance in comparison to the conventional golf clubs. Further, the procedure for imparting the elastic effect to the sole of the club head can be carried out by press working in the same process as that for the conventional golf clubs except that the press die needs to be changed. Therefore, there is no increase in production costs, and the golf club according to the present invention can be produced by the same manufacturing process as that for the conventional golf clubs despite the improvement in performance.

[0093] It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the gist of the present invention.

Claims

1. A golf club having a metallic hollow golf club head, said golf club comprising:

a face member disposed at a front of said club head and having a hitting surface for hitting a golf ball; and

a head body member constituting a remaining part of said club head, said head body member including:

a sole forming a bottom of said club head;

a crown forming a top of said club head;

a toe forming a forepart of said club head;

a heel forming a rear part of said club head;

a back positioned opposite said face member to form a back part of said club head; and

a hosel to which a club shaft is connected;

wherein a deformable area that is elastically deformable in response to hitting of the golf ball on said hitting surface is provided at a joint between a lower end of said face member and said sole.

2. A golf club according to claim 1, wherein said deformable area includes a lower end portion of said face member that is bent at an angle not less than 90 degrees to form a bent portion, said sole being joined to said bent portion, said sole being convexly projected toward the top of said club head in a section taken along a vertical plane containing a line perpendicular to said hitting surface.

3. A golf club according to claim 1, wherein said deformable area includes a lower end portion of said face member that is bent at an angle not less than 90 degrees to form a bent portion, said sole being jointed to said bent portion, said sole being convexly projected away from the top of said club head in a section taken along a vertical plane containing a line perpendicular to said hitting surface.

4. A golf club according to claim 1, wherein said deformable area includes a lower end portion of said face member that is bent at an angle not less than 90 degrees to form a bent portion, said sole being joined to said bent portion, said sole being provided with at least one hole.

5. A golf club according to claim 1, wherein said deformable area includes a lower end portion of said face member that is bent at an angle not less than 90 degrees to form a bent portion, said sole being joined to said bent portion, said sole having a part thereof replaced with a thin plate.

6. A golf club according to claim 1, wherein said deformable area includes a lower end portion of said face member that is bent at an angle not less than 90 degrees to form a bent portion, said sole being joined to said bent portion, said sole being divided into two portions at a part thereof, said two portions being displaceable relative to each other.

7. A golf club according to claim 2 or 3, wherein said sole in said deformable area has a smaller plate thickness than that of said bent portion.

8. A golf club according to claim 2, wherein a part of said sole in said deformable area forms an arch-shaped groove.

9. A golf club according to claim 2, wherein a portion of said sole that is joined to said bent portion in said deformable area forms a groove having a surface approximately parallel to said hitting surface.

10. A golf club according to claim 7, wherein said deformable area has a gentle bend G formed by intersection of a line S1 tangent to a surface of said face member with a line S2 tangent to said bent portion, said bend G having an angle &agr; not less than 90 degrees, and a gentle bend H formed by intersection of said tangent line S2 with a line S3 tangent to a surface of said sole, said bend H having an angle &agr;1 not less than 90 degrees.

11. A golf club according to claim 10, wherein said deformable area has at least one arch-shaped groove provided in a surface of said sole near said bend H, and wherein a gentle bend J is formed by intersection of a line S4 tangent to said groove with said tangent line S2, said bend J having an angle &agr;2 not less than 90 degrees, and a gentle bend K is formed by intersection of a line S5 tangent to said groove with said tangent line S31 said bend K having an angle &agr;3 not less than 90 degrees, wherein said bend G, said bend J and said bend K form a continuous gently curved line.

12. A golf club according to claim 10 or 11, wherein the angle &agr; of said bend G is not less than 90 degrees and not more than 135 degrees, preferably not less than 90 degrees and not more than 120 degrees.