Golf club head

Abstract

A golf club head comprises a face portion defining a clubface for striking a golf ball; the face portion provided in the clubface with a high-resilience part made of a metal material having a Young's modulus E of not less than 29 (GPa) but not more than 107 (GPa); and in a measuring state of the club head which is defined as being placed on a horizontal plane such that a clubshaft center line inclines at its lie angle within a vertical plane and the clubface inclines at its face angle with respect to the vertical plane, a moment of inertia of the club head around a horizontal axis passing a gravity point of the club head in parallel with the vertical plane, being not less than 1600 (g·sq.cm) but not more than 4000 (g·sq.cm).

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a golf club head being capable of increasing the carry.

[0002] The laid-open international application WO98/46312 discloses a golf club head, wherein in order to increase the traveling distance of struck golf balls, a metal material having a relatively low Young's modulus is used in the face portion according to the so-called impedance matching theory. In this theory, the mechanical impedance of the clubface is lowered to near that of the golf balls in the expectation that the loss of the impact energy which transfers from the club head to the hit ball is minimized and as a result the initial speed of the hit ball is increased.

[0003] When a golf ball is hit at a sweet spot of the clubface, the traveling distance (carry and run) effectively increases. However, if the hitting point is off the sweet spot towards the crown or sole, there is a tendency for the carry loss to become considerably large contrary to expectation.

[0004] FIG. 8 shows results of an experiment in which several kinds of club heads were made changing the Young's modulus of the face portion, and the backspin of the hit ball was measured by hitting the golf ball at the sweet spot and also an upper point and a lower point at a distance of 10 mm from the sweet spot towards the crown and the sole, respectively. As shown in this graph, as the Young's modulus of the face portion is decreased, backspin increases at an accelerating pace in case of the lower hitting, but in case of the upper hitting backspin decreases at an accelerating pace. Thus, in this kind of club head having a low Young's modulus in the clubface, a vertical gear effect appears strongly than the club heads having normal Young's modulus. Here, the vertical gear effect is the following phenomenon. When a golf ball is struck off the sweet spot SS as shown in FIG. 9, a moment of rotation whose magnitude is substantially equal to the product of the impact force F and distance L1, L2 is produced on the club head (a) around its gravity point G, and the club head rotates around a horizontal axis passing the gravity point G by a minute angle in a moment. As a result, the struck ball (b) receives a force in the opposite direction to the rotational direction of the club head (a).

[0005] Thus, in case of lower hitting, the backspin is excessively increased and the trajectory becomes high to increase the carry loss.

SUMMARY OF THE INVENTION

[0006] It is therefore, an object of the present invention to provide a golf club head, in which a vertical gear effect is effectively controlled to increase the carry although the Young's modulus of the face portion is low.

[0007] According to the present invention, a golf club head comprises

[0008] a face portion defining a clubface for striking a golf ball,

[0009] the face portion provided in the clubface with a high-resilience part made of a metal material having a Young's modulus E of not less than 29 (GPa) but not more than 107 (GPa),

[0010] in a measuring state of the club head which is defined as being placed on a horizontal plane such that a clubshaft center line inclines at its lie angle within a vertical plane and the clubface inclines at its face angle with respect to the vertical plane, a moment of inertia of the club head around a horizontal axis passing a gravity point of the club head in parallel with the vertical plane, being not less than 1600 (g·sq.cm) but not more than 4000 (g·sq.cm).

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a perspective view of a golf club head according to the present invention.

[0013] FIG. 2 is a front view thereof.

[0014] FIG. 3 is a top view thereof.

[0015] FIG. 4 is a sectional view thereof taken along vertical plane VP2 shown in FIG. 3.

[0016] FIG. 5 is a sectional view thereof taken along a line A-A shown in FIG. 3.

[0017] FIG. 6 is an exploded perspective view thereof.

[0018] FIGS. 7 a and 7b are schematic overhead views for explaining insufficient return and full return of the clubface at the time of striking a golf ball.

[0019] FIG. 8 is a graph showing a relationship between the backspin and hitting position as a function of the Young's modulus.

[0020] FIG. 9 is a cross sectional view of a club head for explaining the vertical gear effect.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0021] Embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings.

[0022] In the drawings, golf club head 1 according to the present invention is a wood-type golf club head for number 1 driver.

[0023] The club head 1 comprises a face portion 3 defining a clubface 2 for striking a golf ball, a crown portion 4 defining a top face of the club head intersecting the clubface 2 at the upper edge 2a thereof, a sole portion 5 defining a bottom face of the club head intersecting the clubface 2 at the lower edge 2b thereof, a side portion 6 between the crown portion 4 and sole portion 5, which extends from the toe-side edge 2t to the heel-side edge 2e of the clubface 2 through the back of the club head, and a hosel portion 7 provided with a clubshaft-inserting hole 7a.

[0024] The clubshaft-inserting hole 7a has an opening for the clubshaft (not shown) at the top, and extends to the inside of the clubhead as shown in FIG. 5. The center line CL (hereinafter the “clubshaft center line CL”) is used to determine the undermentioned various positions and orientation of the club head. The clubshaft-inserting hole 7a in this example is circular and terminated in the cavity (i).

[0025] In FIGS. 1-5, the club head 1 is in its measuring state. The measuring state is such that, as shown in FIG. 2 and FIG. 3, the club head 1 is placed on a horizontal plane HP, so that the clubshaft center line CL inclines at its lie angle β within a vertical plane VP1, and the clubface 2 inclines at its face angle β with respect to the vertical plane VP1. Here, the face angle β is the angle between the vertical plane VP1 and a horizontal tangential line N to the centroid or center of FIG. 2c of the clubface 2.

[0026] In this embodiment, as shown in FIG. 6, the club head 1 is made up of a main body 1A having an opening O on the front thereof, and a face member 1B which is fixed on the front of the head main body 1A so that the opening O is closed and the closed cavity (i) is formed. Thus, behind the face portion 3, a hollow is formed.

[0027] The head main body 1A in this example comprises the crown portion 4, sole portion 5, side portion 6, hosel portion 7 and an annular periphery part 9 of the face portion 3 of which inner edge defines the above-mentioned opening O.

[0028] As to the material of the head main body 1A, metal materials such as aluminum alloys, pure titanium, titanium alloys, and stainless steel can be used. Preferably a titanium alloy whose specific tensile strength is high is used. In this example, the head main body 1A is made of a titanium alloy Ti-6Al-4V through a lost-wax precision casting process. Aside from metal materials, fiber reinforced resins or plastics may be used too.

[0029] The face member 1B in this example is a slightly curved plate of which front surface defines almost entirety of the clubface 2 because the above-mentioned annular periphery part 9 is very narrow in width. The face member 1B is fitted in the opening O and fixed by an appropriate way such as adhesive agent, welding, caulking and press fitting.

[0030] AS shown in FIG. 4, the back face 11 of the face member 1B is supported by a ledge 9a provided on the head main body 1A along the inner edge of the periphery part 9. The back-supported area is preferably set in a range of from 2 to 20%, preferably 2 to 10%, more preferably 2 to 5% of the overall area s of the clubface 2. The ledge 9a in this example is continuously formed along the inner edge, but it can be formed at intervals. Instead of the continuous or discontinuous ledge 9a supporting the periphery of the back face 11, a support for the entirety of the back face 11 may be provided. Further, it may be possible to omit such back support.

[0031] In this embodiment, a high-resilience part 8 is formed in the face portion 3 by the face member 1B.

[0032] The high-resilience part 8 has a Young's modulus E which is not less than 29 GPa, preferably not less than 39 GPa, more preferably not less than 49 GPa, still more preferably not less than 58 GPa, but not more than 107 GPa, preferably not more than 98 GPa, more preferably not more than 88 GPa, still more preferably not more than 78 GPa.

[0033] Thus, the face member 1B is made of a metal material having such Young's modulus E.

[0034] If the Young's modulus E is increased over 107 GPa, the impedance of the clubface increases over that of balls, and the effect to increase the initial velocity of the ball is lessened. If the Young's modulus E is decreased under 29 GPa, it becomes difficult to provide durability for the face portion.

[0035] For the metal material of the face member 1B, various alloys may be used, but amorphous alloys and titanium alloys are preferably used. AS to the amorphous alloys, for example, zirconium alloys are preferably used for the workability and the like. On the other hand, in case of crystalloid alloys, titanium-zirconium alloys are preferably used.

[0036] The thickness t of the high-resilience part 8 or the face member 1B in this embodiment is preferably not less than 1.0 mm, more preferably not less than 1.5 mm, still more preferably not less than 2.0 mm, but preferably not more than 3.5 mm, more preferably not more than 3.0 mm, still more preferably not more than 2.8 mm, yet still more preferably not more than 2.5 mm. If the thickness t is less than 1.0 mm, the strength and durability are liable to become insufficient. If the thickness t is more than 3.5 mm, the clubface becomes rigid, and the effect to increase the carry becomes lessened.

[0037] As to the thickness of the face portion 2 (including the face member in this embodiment), on the other hand, it is preferable that the thickness satisfies the above-mentioned limitation of the thickness t through the entirety of the face portion 2 if possible.

[0038] Further, it is preferable that the product (t·E) of the Young's modulus E (GPa) and the thickness t (mm) is not less than 77 (GPa·mm), more preferably not less than 86 (GPa·mm), still more preferably not less than 96 (GPa·mm), but not more than 245 (GPa·mm), more preferably not more than 231 (GPa·mm), still more preferably not more than 221 (GPa·mm).

[0039] If the product (t·E) is less than 77 (GPa·mm), the strength and durability of the clubface are liable to become insufficient. If more than 245 (GPa·mm), the clubface becomes rigid, and the effect to increase the carry becomes lessened.

[0040] In this example, the thickness t is substantially constant, but if varied, the area mean value (namely, a value which is obtained by weighting the thickness with area and then averaging the weighted thickness, more specifically, a value obtained by dividing the volume by the area) is used as the thickness t in calculating the product (t·E).

[0041] As to the materials of the club head, it is possible that the entirety of the club head (in this embodiment, both of the main body 1A and face member 1B) is made of the same metal material having the above-mentioned Young's modulus.

[0042] Further, the club head 1 has a moment of inertia (I) which is not less than 1600 (g·sq.cm), preferably not less than 1800 (g·sq.cm), more preferably not less than 2000 (g·sq.cm), still more preferably not less than 2200 (g·sq.cm), but not more than 4000 (g·sq.cm), preferably not more than 3500 (g·sq.cm), more preferably not more than 3100 (g·sq.cm).

[0043] Here, the moment of inertia (I) is that around a horizontal axis HL which passes through the gravity point G of the club head in parallel with the above-mentioned vertical plane VP1, and it is measured including the coating of the head if any, but the clubshaft, ferrule and the like are not included.

[0044] By setting the moment of inertia (I) in a relatively high range as above, if hitting a golf ball off the sweet spot SS as shown in FIG. 9, the rotation of the club head 1 around the horizontal axis HL is prevented or effectively decreased and the vertical gear effect can be effectively controlled.

[0045] If the moment of inertia (I) is more than 4000 (g·sq.cm), the size of the club head is inevitably increases, and it becomes hard to handle the club.

[0046] The moment of inertia (I) of the club head 1 can be increased by a) increasing the head volume, b) increasing the wall thickness of the club head away from the gravity point, c) increasing the specific gravity of the club head away from the gravity point, and/or d) decreasing the roll radius of the clubface.

[0047] From this point of view, it is preferable that the head volume is not less than 280 cc, more preferably not less than 290 cc, still more preferably not less than 300 cc, but not more than 450 cc, more preferably not more than 420 cc, still more preferably not more than 400 cc.

[0048] As to the clubface 2, the maximum horizontal width FW thereof is preferably set in a range of from 85 to 110 mm more preferably 90 to 106 mm, and the maximum vertical height FH thereof is preferably set in a range of from 40 to 65 mm more preferably 45 to 60 mm.

[0049] The area of the above-mentioned high-resilience part 8 is set to be more than 65%, preferably more than 75%, more preferably more than 85%, still more preferably more than 95% of the area of the clubface 2.

[0050] The clubface 2 is, as shown in FIG. 3, provided with a bulge whose radius R1 is in a range of from 254 to 304.8 mm, preferably 279.4 to 292.1 mm. Further, as shown in FIG. 4, the clubface 2 is provided with a roll whose radius R2 is in a range of from 228.6 to 330.2 mm, preferably 254 to 304.8 mm. Here, the radius R2 is defined in the above-mentioned measuring state as the radius of curvature of the clubface 2 at a second vertical plane VP2 which includes the center 2c of figure of the clubface 2 and is perpendicular to the vertical plane VP1. By setting the roll radius R2 as above, the vertical gear effect can be reduced.

[0051] Further, the club head 1 has a gravity point distance c which is not less than 26 mm, preferably not less than 28 mm, more preferably not less than 30 mm, but not more than 40 mm, preferably not more than 38 mm, more preferably not more than 36 mm, still more preferably not more than 34 mm.

[0052] Here, the gravity point distance c is, as shown in FIG. 3 and FIG. 5, the shortest distance between the clubshaft center line CL and the projected point Ga of the gravity point G on the vertical plane VP1 under the measuring state.

[0053] If the gravity point distance C is more then 40 mm, the so called “return” of the club head 1 is liable to become insufficient as shown in FIG. 7a when striking the ball.

[0054] Therefore, in case of a golfer who hits right-handed, the ball is liable to curve to the right.

[0055] If the gravity point distance c is less than 26 mm, a moment of inertia of the club head around the clubshaft center line excessively decreases. As a result, unfavorably the carry is greatly varied depending on the ball hitting point.

[0056] By setting the gravity point distance C as above, the club head 1 can easily and fully return to the original position prepared for the stroke as shown in FIG. 7b. As a result, a draw shot to increase the carry becomes easy even for average golfers.

[0057] Comparison Test

[0058] Changing the face member material, Young's modulus E, product (E×t), moment of inertia and gravity point distance as shown in Table 1, several kinds of wood-type golf club heads having the structure shown in FIGS. 1 to 6 were made. The moment of inertia and gravity point distance were adjusted by attaching weight to appropriate part of the inside of the head main body such as the backside of the side portion, hosel portion, toe and sole portion. The moment of inertia (I) was measured with a moment-of-inertia measurement instrument made by Inertia Dynamics, Inc. The heads were attached to carbon shafts (FLEX R) and 45-inch drivers were made, and the following tests were conducted.

[0059] Hitting Test 1

[0060] Each club was attached to a swing robot, and three-piece balls (MAXFLI HI-BRID, Sumitomo Rubber Ind., Ltd.) were struck at a head speed of 40 m/s five times per each of three hitting positions in each club to obtain mean values of the respective backspin, initial velocity and travelling distance (carry and run). Here, the three hitting positions are a sweet spot of the clubface (sweet spot hit), an upper position 10 mm upward from the sweet spot (upper hit), and a lower position 10 mm downward from the sweet spot (lower hit).

[0061] Hitting Test 2

[0062] Each of ten golfers whose handicaps ranged from 2 to 11 struck balls ten times per club. The distance of the landing position of the hit ball was measured from the line in the aimed projectile direction of the golf ball. The measured distance is indicated in meter in Table 1 as the mean value of the ten persons. Thus, the smaller value is better and means that the direction stability is good.

TABLE 1
Head	Ref. 1	Ref. 2	Ref. 3	Ref. 4	Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5	Ex. 6	Ex. 7
Head volume	(cc)	270	270	270	270	270	270	270	270	270	270	270
Face portion	Max. width = 94 mm, Max. height = 47 mm,
	Bulge radius = 304.8 mm, Roll radius = 304.8 mm
Face member
Material *1		A	B	C	D	A	A	A	A	A	B	B
Young's modulus E	(GPa)	69	98	118	196	69	69	69	69	69	98	98
Thickness t	(mm)	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8	2.8
Product (E × t)	(GPa · mm)	193.2	274.4	330.4	548.8	193.2	193.2	193.2	193.2	193.2	274.4	274.4
Moment of inertia I	(g · sq.cm)	1500	1500	1500	1500	2000	3000	3000	3000	3000	2000	2000
Gravity point distance C	(mm)	36	36	36	36	36	36	34	32	43	36	32
Back spin	(rpm)
Upper hit		1621	1706	1726	1720	2013	2115	2111	2113	2009	2121	2123
Sweet spot hit		2612	2733	2741	2763	2544	2659	2661	2662	2543	2603	2610
Lower hit		3624	3434	3359	3307	3026	3011	3002	3006	3030	3013	3001
Initial velocity	(m/s)
Upper hit		57.1	56.8	56.2	55.8	57.4	57.7	57.7	57.8	57.7	56.9	58.1
Sweet spot hit		58.7	58.3	57.9	57.4	58.7	58.8	58.7	58.7	58.7	58.4	59.1
Lower hit		57.6	57.1	57	56.4	57.9	58.2	58.3	58.2	58.2	57.2	58
Carry and Run	(m)
Upper hit		246.3	237.8	235.8	233.1	241	240.9	241	241.1	241.6	237.7	237.6
Sweet spot hit		236.6	234.5	228.2	224.5	236.9	236.2	237.6	237.5	237	234.4	234.5
Lower hit		217.3	217.5	217.4	217.2	220.6	223.2	230.8	233	222.9	220.5	224.9
Distance of	(m)	13	14.3	16.2	18.5	9.1	8.2	5.3	3.3	12.3	5.7	4.3
Landing position
*1 A: Zr54Al10Cu30Ni5Hf1, B: Zr60Al10Cu20Ni10, C: Ti-6A1-4V, D: SUS630

[0063] T focus attention on the test results of the sweet spot hitting, as the Young's modulus became smaller, the initial velocity of the hit ball became higher and the carry became longer. Thus, the rebound performance of the club head was improved.

[0064] In case of a small moment of inertia such as Ref., the carry loss became increased in the lower hit in comparison with the sweet spot hit. It is believed that the backspin was greatly increased by a strong vertical gear effect.

[0065] In Examples 1 and 2 whose moment of inertia was larger than Ref.1, the carry loss became small in the lower hit in comparison with the sweet spot hit. It is believed that the backspin was prevented from increasing even in the lower hit, and the vertical gear effect was effectively controlled.

[0066] Incidentally, in case of the driver, backspin of a hit ball which is preferable for obtaining a desirable ballistic course is about 2000 to 3100 rpm. The backspin in Examples satisfied this range in each of the sweet spot hit, upper hit and lower hit. Thus, the carry can be improved.

[0067] In case of a relatively short gravity point distance such as Examples 3 and 4, variation in the landing positions of the hit balls was decreased and the directional stability was improved. Thus, it is believed that the return of the club head was improved.

[0068] The present invention can be suitably applied to wood-type golf club heads as explained above, but it can be also applied to various club heads such as iron-type and utility-type as far as a hollow is formed behind the clubface.

Claims

1. A golf club head comprising a face portion defining a clubface for striking a golf ball, the face portion provided in the clubface with a high-resilience part made of a metal material having a Young's modulus E of not less than 29 (GPa) but not more than 107 (GPa), in a measuring state of the club head which is defined as being placed on a horizontal plane such that a clubshaft center line inclines at its lie angle within a vertical plane and the clubface inclines at its face angle with respect to the vertical plane, a moment of inertia of the club head around a horizontal axis passing a gravity point of the club head in parallel with the vertical plane, being not less than 1600 (g·sq.cm) but not more than 4000 (g·sq.cm).

2. A golf club head according to claim 1, wherein the product (t·E) of the Young's modulus E (GPa) and a thickness t (mm) of the high-resilience part is not less than 77 (GPa·mm) but not more than 245 (GPa·mm).

3. A golf club head according to claim 1 or 2, wherein in the measure state, a gravity point distance which is defined as the shortest distance between the clubshaft center line and a projected point of the gravity point on the vertical plane, is not less than 26 mm bot not more than 40 mm.