Patent Grant
7494426
The present invention relates to a golf club head having a face backside thereof reinforced with ribs.
Recently, the golf club heads are becoming larger in size but smaller in thickness, so that a face portion tends to suffer insufficient strength. A method of affixing the ribs to the face backside has been known as a measure for meeting the purposes of reducing the thickness of the face and increasing the strength thereof.
Japanese Unexamined Patent Publication No. 2003-290396 (Claim 1, Claim 2, FIG. 1, FIG. 2) discloses a golf club head wherein a plurality of ribs are provided as extended vertically, wherein the ribs located closer to a toe-side and a heel-side are accordingly decreased in height and wherein the individual ribs have a constant height distribution with respect to a longitudinal direction thereof or heights progressively increased toward a bottom side (sole side).
In spite of a great rib volume (rib weight), the above prior-art golf club head fails to achieve a sufficient face-strength reinforcing effect (hereinafter, referred to as “face reinforcement effect” or simply as “reinforcement effect”). Since all the ribs are extended in the vertical direction, the face is excessively increased in rigidity particularly at its toe-side and heel-side because of the ribs extended in the vertical direction. As a result, face vibration is excessively limited at impact with a ball.
It is an object of the invention to provide a golf club head featuring high restitution performance while maintaining the sufficient face reinforcement effect by way of the ribs.
A golf club head according to the invention comprises six or more ribs disposed on a face backside, the ribs being extended from a face center toward face circumferences, wherein an angle θ(°) between extension directions of adjoining ones of the ribs is less than 90°, and wherein one of the ribs that forms the smallest angle between its extension direction and a head vertical direction and that extends from the face center toward a crown-side face circumference constitutes an upward rib, which has a smaller cross-sectional area than any of those of the other ribs.
The ribs are laid from the face center toward the face circumferences, thereby diffusing stress exerted on the face more uniformly without excessively increasing the face rigidity. The reason for providing six or more ribs is because if the number of ribs is less than six, rib-free regions are so large that the face tens to suffer the insufficient strength at the rib-free regions. The angle θ between the extension directions of adjoining ones of the ribs is defined to be less than 90° for the following reason. If there is a region having the angle θ of 90° or more, the region tends to suffer the insufficient strength. Furthermore, the aforementioned upward rib is configured to have a relatively small cross-sectional area, whereby the head may be increased in the restitution performance as maintaining the face reinforcement effect.
The head vertical direction is defined as follows.
In a standard state where the head is placed on the horizontal plane at a predetermined loft angle (real loft angle) and a predetermined lie angle, the head vertical direction is defined as a direction of line of intersection between a reference plane and a face surface, the reference plane being defined to include a perpendicular line drawn from a gravity center of the head to the face surface and meets at right angles with the horizontal plane.
On the other hand, the cross-sectional area of the rib is defined as follows.
Provided that a position A is defined to be spaced away from a longitudinal center position of the rib toward one end thereof by a distance of 40% of the overall length thereof (which means hereinafter the overall longitudinal length of the rib) and that a position B is defined to be spaced away from the longitudinal center position of the rib toward the other end thereof by a distance of 40% of the overall length thereof, the cross-sectional area of the rib is defined as a mean value of the cross-sectional areas as determined at longitudinal positions between the position A and the position B.
The cross-sectional area of the aforesaid upward rib may preferably be 2.0 mm2 or more. If the cross-sectional area is less than 2.0 mm2, the face is prone to fracture because of the insufficient face strength. Therefore, the cross-sectional area of the upward rib may more preferably be 4.0 mm2 or more, even more preferably 4.1 mm2 or more and particularly preferably 4.3 mm2 or more. In addition, the cross-sectional area of the upward rib may preferably be 8.0 mm2 or less. If the cross-sectional area exceeds 8.0 mm2, the face is excessively increased in the rigidity so that the face vibration is excessively reduced and the restitution performance tends to decrease. Therefore, the cross-sectional area of the upward rib may more preferably be 6.0 mm2 or less and particularly preferably 5.8 mm2 or less.
The cross-sectional area of each of the other ribs than the upward rib may preferably be 4.0 mm2 or more. If the cross-sectional area of each of the other ribs is less than 4.0 mm2, the face is prone to fracture because of the insufficient face strength. Therefore, the cross-sectional area of each of the other ribs may more preferably be 5.0 mm2 or more, even more preferably 5.8 mm2 or more and particularly preferably 6.1 mm2 or more.
In addition, the cross-sectional area of each of the other ribs than the upward rib may preferably be 10.0 mm2 or less. If the cross-sectional area of each of the other ribs exceeds 10.0 mm2, the face is excessively increased in the rigidity so that the face vibration is excessively reduced and the restitution performance tends to decrease. Therefore, the cross-sectional area of each of the other ribs may more preferably be 8.0 mm2 or less, even more preferably 7.6 mm2 or less and particularly preferably 7.5 mm2 or less. In a case where two upward ribs are provided, the cross-sectional area of the upward rib is defined as a mean value of the cross-sectional areas of the two ribs.
The aforesaid ribs may preferably have widths of 3 mm to 14 mm and heights of 0.3 mm to 1.5 mm. If the rib width is smaller than 3 mm, the stress tends to concentrate on a rib having a relatively small width so that the rib is prone to fracture at an edge portion thereof. If the rib width is greater than 14 mm, the face is excessively increased in the rigidity and the restitution performance tends to decrease. If the rib height is smaller than 0.3 mm, the face reinforcement effect by way of the ribs is decreased. If the rib height is greater than 1.5 mm, the stress tends to concentrate on the rib.
In the aforementioned golf club head, a face thickness may preferably be 0.5 mm or more and 3.5 mm or less. If the face thickness is less than 0.5 mm, the face tends to be reduced in the face strength. If the face thickness exceeds 3.5 mm, the face is excessively increased in the rigidity so that the restitution performance may be reduced.
In the above golf club head, a roundness of a curvature radius R(mm) may preferably be imparted to an intersection of boundary lines of a respective pair of adjoining ones of the ribs. The value of a ratio (θ/R) between the curvature radius R(mm) and the angle θ(°) between the adjoining ribs may preferably be in the range of 3 to 50. If the value of (θ/R) is less than 3, the curvature radius R is too great relative to the angle θ and hence, the face is excessively increased in a thick area so that the restitution coefficient tends to decrease. On the other hand, if the value of (θ/R) exceeds 50, the curvature radius R is too small relative to the angle θ and hence, the face is decreased in the thick area while the stress tends to concentrate on the intersection of the boundary lines. Hence, the head tends to be reduced in durability.
According to the invention as described above, six or more ribs are provided as extended from the face center toward the face circumferences, and the upward rib is configured to have the smaller cross-sectional area than that of each of the other ribs. Therefore, the head of the invention is adapted to achieve the increased restitution performance as maintaining the face reinforcement effect.
Preferred embodiments of the invention will hereinbelow be described with reference to the accompanying drawings.
The head 1 is formed from a metal such as a titanium alloy, having a two-piece structure wherein two members are bonded together. In
The invention does not particularly limit the material of the head 1. For example, a variety of metals, fiber-reinforced plastics and the like are usable. Examples of the usable metal include titanium, titanium alloys, stainless steel alloys, aluminum alloys, magnesium alloys and the like. These metal materials may be used alone or in combination of plural types. Examples of a usable titanium alloy include 6Al-4V titanium, 15V-3Cr-3Al-3Sn titanium, 15Mo-5Zr-3Al titanium, 13V-11Cr-3A1 titanium and the like. Beta titanium alloys having high strength, in particular, may favorably be used for forming the face portion 2. Examples of a usable fiber-reinforced plastic include plastics reinforced with carbon fiber. The face portion 2 may use a rolled material or a forged material so as to increase the strength, whereas the other portions may use cast articles having high design freedom. Then, these portions may be unified by welding. This method is preferred from the viewpoint of achieving both the strength and the higher freedom of configuration design. On the other hand, a plastic reinforced with carbon fiber may be used for forming a part or the whole body of the crown portion 3, while the other portions may be formed by forging metals. This method is preferred in terms of ease of setting a low gravity center.
The head 1 has the hollow structure as described above. The face portion 2 includes: a face surface 2a defining an outside surface thereof and contacting a ball at impact with the ball; and a face backside 2b defining an inside surface of the face surface or the backside of the face surface 2a.
As shown in
In the head 1, an angle between extension directions (represented by broken lines in
While boundary lines rk each dividing the rib portion from a non-rib portion are present on widthwise opposite sides of each of the ribs 71 to 76, an intersection of the boundary lines rk of the adjoining ribs is rounded (chamfered) to impart a roundness of a curvature radius R=1 to 15 mm. Specifically, as shown in
In such a configuration, the head is increased in durability because a thick area of the face is increased by virtue of the roundnesses imparted to the respective intersections of the boundary lines of the adjoining ribs and because stress concentration on the intersections is reduced. The reason for defining the curvature radius R to be 1 mm or more is as follows. If the curvature radius R1 is less than 1 mm, the durability tends to decrease because the effects to increase the thick area and to reduce the stress concentration are reduced. Therefore, the curvature radius R may more preferably be 2 mm or more. The reason for defining the curvature radius R to be 15 mm or less is as follows. If the curvature radius exceeds 15 mm, the thick area of the face is increased so much that the restitution coefficient tends to decrease. Therefore, the curvature radius R may more preferably be 14 mm or less and particularly preferably 12 mm or less.
The meaning of “the roundness of the curvature radius R of Xmm or more” and “the roundness of the curvature radius R of Ymm or less” herein are explained by way of example of the adjoining ribs 72 and 73 according to the embodiment of
“The roundness of a curvature radius R2 of Xmm or more” means that a curved line of the curvature radius R2 is farther away from the center position rc of the rib intersection than a curved line m1 which is smoothly continuous to both of the boundary lines rk of the ribs 72, 73 intersecting each other, which is protruded toward the center position rc of the rib intersection and which has the curvature radius of Xmm.
“The roundness of the curvature radius R2 of Ymm or less” means that the curved line of the curvature radius R2 is closer to the center position rc of the rib intersection than a curved line m2 which is smoothly continuous to both of the boundary lines rk of the ribs 72, 73 intersecting each other, which is protruded toward the center position rc of the rib intersection and which has the curvature radius of Ymm.
The above roundness need not define an arc having a single curvature radius and may also define a combination of arc portions having different curvature radii. In the case of the roundness defining a combination of arc portions having different curvature radii, it is preferred from the viewpoint of durability and restitution that the roundness does not include an arc portion having a curvature radius R of less than 0.5 mm. It is more preferred that the roundness does not include an arc portion having a curvature radius R of less than 1.0 mm. In addition, it is preferred that the roundness does not include an arc portion having a curvature radius R of more than 20 mm. It is more preferred that the roundness does not include an arc portion having a curvature radius R of more than 15 mm. Considering stress diffusion at the intersection of the boundary lines rk, it is most preferred that the above roundness has a single R (single curvature radius).
The value of a ratio (θ/R) between the above curvature radius R(mm) and the angle θ(°) between the ribs is defined to be 3 to 50. Specifically, the value (θ1/R1) of a ratio between the above curvature radius R1 (mm) and the angle θ1(20) is defined to be 3 to 50. Likewise, the respective values of (θ2/R2), (θ3/R3), (θ4/R4), (θ5/R5), (θ6/R6) are also defined to be 3 to 50. The reason for defining the value of (θ/R) to be 3 or more is because if the value of the ratio is less than 3, the curvature radius. R is so great relative to the angle θ that the face is excessively increased in the thick area and hence, the restitution coefficient tends to decrease. Therefore, the value of (θ/R) may more preferably be 6 or more. The reason for defining the value of (θ/R) to be 50 or less is because if the value of the ratio exceeds 50, the curvature radius R is so small relative to the angle θ that the stress tends to concentrate on the intersection of the boundary lines and hence, the durability tends to decrease. Therefore, the value of (θ/R) may more preferably be 22 or less.
It is preferred to define a relationship:
R(1)≧R2≧ . . . ≧R(m) and R(1)>R(m), (a)
provided that the aforesaid plural angles θ are represented by θ(1), θ(2), . . . , θ(m) in the descending order of the values thereof, and that an inter-rib curvature radius R with respect to the angle θ(1) is represented by R(1), an inter-rib curvature radius R with respect to the angle θ(2) is represented by R(2), . . . , and an inter-rib curvature radius R with respect to the angle θ(m) is represented by R(m). It is more preferred to define a relationship:
R(1)>R(2)> . . . >R(m). (b)
As described above, it is preferred to limit the value of the ratio (θ/R) to the predetermined range. Therefore, the relation between the curvature radius R and the angle θ may be optimized by defining the magnitude relations between the curvature radii R and the angles θ as illustrated by the above expressions (a) and (b).
It is noted that the individual values of the curvature radii in the above expressions (a) and (b) are expressed in millimeters and are rounded off to the whole numbers.
Out of the ribs 71 to 76, an upward rib 7 (equivalent to the rib 71 in this embodiment) has a smaller cross-sectional area than that of each of the other ribs 72 to 76. The upward rib forms the smallest angle between its extension direction and a head vertical direction d1 (indicated by the chain double-dashed line in
While the cross-sectional area of the rib is defined in the foregoing, the cross-sectional area of the rib will be more specifically described with reference to the drawing.
It is preferred that a cross-sectional area of the rib as determined at place shifted from the position A toward the rib end and a cross-sectional area thereof as determined at place shifted from the position B toward the rib end are each greater than the above cross-sectional area of the rib (the mean value of the cross-sectional areas as determined at longitudinal positions between the position A and the position B). This is because the stress tends to concentrate particularly on the rib ends.
As described above, the ribs 71 to 76 are laid from the face center toward the face circumferences, thereby diffusing the stress exerted on the face more uniformly without excessively increasing the rigidity of the face.
The reason for providing six or more ribs is because if the number of ribs is less than six, rib-free regions are so large that the regions tend to suffer the insufficient strength. However, if the number of ribs is excessive, the face may be excessively increased in the rigidity so that the restitution performance may be lowered. Therefore, the number of ribs extended from the face center toward the face circumferences may preferably be 15 or less, more preferably 10 or less and particularly preferably 8 or less.
The angles θ1 to θ6 between the extension directions of the respective pairs of adjoining ribs are defined to be less than 90° for the following reason. If there exists a region having any one of the angles θ1 to θ6 that is 90° or more, the region tends to suffer the insufficient strength. Therefore, the angle may preferably be 80° or less. However, if the angle is too small, a region having such a small angle may be excessively increased in the rigidity so that the restitution performance may be lowered. Therefore, the angle between the extension directions of the respective pairs of adjoining ribs may preferably be 15° or more, more preferably 30° or more and particularly preferably 40° or more.
The upward rib 7 is configured to have the smaller cross-sectional area than that of each of the other ribs 72 to 76, whereby the head may achieve an increased restitution performance while maintaining the face reinforcement effect. The reason is as follows. A crown-side region from the face center has a wider margin of face strength than the other regions of the face. Therefore, the upward rib 7 configured to have the smaller cross-sectional area than that of each of the other ribs 72 to 76 exerts a smaller influence on the face reinforcement effect than a configuration where the cross-sectional areas of the other ribs 72 to 76 are decreased. On the other hand, a face width between the face center and the crown portion is relatively small. Hence, the rigidity at the crown-side region from the face center has a relatively great influence on the flexure of the overall face. Therefore, the upward rib 7 is configured to have the smaller cross-sectional area than that of each of the other ribs 72 to 76, whereby the head is effectively increased in the restitution performance while maintaining the face reinforcement effect.
A center 15c (a centroid or gravity center) of a rib convergence portion 15 (represented by hatched broken lines) shown in
Individual widths W1 to W6 of the ribs 71 to 76 may preferably be in the range of 3 mm to 14 mm. If the rib width is less than 3 mm, the stress may be concentrated on a rib having a relatively small width so that the rib may be prone to fracture at an edge portion thereof. Therefore, the rib width may more preferably be 5 mm or more and particularly preferably 7 mm or more. The rib width is defined to be 14 mm or less for the following reason. If the rib width is more than 14 mm, the face is excessively increased in the rigidity so that the restitution performance tends to decrease. Therefore, the rib width may more preferably 12 mm or less, even more preferably 10 mm or less and particularly preferably 8 mm or less.
Individual heights t1 to t6 (
A value given by dividing the rib height by the rib width [(rib height)/(rib width)] may preferably be 0.20 or less and more preferably 0.15 or less. If this value is excessive, the stress tends to be concentrated on the rib portion so that the stress diffusion may be reduced. In addition, the rib portion is excessively increased in the rigidity so that the face may be excessively reduced in the flexure and the restitution performance may be lowered. However, if the value of [(rib height)/(rib width)] is too small, a region increased in thickness by the rib is so large that the face may be reduced in the flexure, or the rib has such a small height that the face reinforcement effect may be reduced. Therefore, the value may preferably be 0.05 or more, more preferably 0.08 or more and particularly preferably 0.10 or more.
It is preferred that a face thickness (the thickness at the face portion 2) may preferably be 0.5 mm or more and 3.5 mm or less. The reason for defining the face thickness to be 0.5 mm or more is because the face having a thickness of less than 0.5 mm tends to suffer the insufficient strength. Therefore, the face thickness may more preferably be 1.0 mm or more and particularly preferably 1.5 mm or more. The reason for defining the face thickness to be 3.5 mm or less is because the face having a thickness of more than 3.5 mm is excessively increased in the rigidity, so that the restitution performance may be reduced. Therefore, the face thickness may more preferably be 3.0 mm or less and particularly preferably 2.7 mm or less.
A face thickness as determined at the rib-free region may preferably be 3.0 mm or less, more preferably 2.5 mm or less and particularly preferably 2.2 mm or less. Despite the reduced thickness at the rib-free region, the face may maintain the strength by virtue of the ribs disposed according the invention. Furthermore, it becomes easier to achieve the increased restitution performance when the face thickness is decreased. It is noted however that if the face is excessively reduced in thickness, the face may suffer the insufficient strength. Therefore, the face thickness at the rib-free region may preferably be 0.4 mm or more, more preferably 0.8 mm or more and particularly preferably 1.4 mm or more.
While the individual ribs 71 to 76 may be extended from the face center toward the face circumferences, the face-center-side ends of the ribs 71 to 76 may preferably be located within 4 mm from the center of the face backside 2b (the unillustrated centroid or gravity center of the face backside 2b). If the distance between the face-center-side end of the rib and the center of the face backside 2b is increased, the reinforcement effect by way of the ribs may fall short at an area around the face center which is most subjected to the stress. In addition, the ribs are reduced in the ability to uniformly diffuse the stress on the face center to the face circumferences.
Each of the ribs 71 to 76 may preferably be extended to place within 5 mm from the face outside circumference gs (the outside circumference of the face backside 2b). It is more preferred that the ribs are extended to the face outside circumference gs. If the distance between the face-circumference-side end of the rib and the face outside circumference gs is increased, the stress on the face center tends to be diffused to a limited area of the face circumferences. In addition, the reinforcement effect by way of the ribs may fall short at the face circumference.
Golf club heads were fabricated according to Examples 1 to 10 as the examples of the invention and according to Comparative Examples 1 to 3. The effects of the invention were examined by evaluating these golf club heads.
All the examples (Examples 1 to 10 and Comparative Examples 1 to 3) had the same specifications except for thickness distributions of the face portion. In the specifications common to the all examples, the examples used a titanium-alloy head which had the hollow structure including the cup-face substantially shaped like a cup and the head body combined with the cup-face by welding, just as in the aforementioned embodiment. The head had a volume of 405 cc and a face area (area of the face surface) of 4200 mm2.
As to Examples 1 to 10, the rib-free region of the face portion had a thickness of 1.8 mm to 2.0 mm. All the ribs of Examples 1 to 10 were configured such that, as shown in
On the other hand, the face backside 2b of Comparative Example 1 is shown in a plan view of
On the other hand, the cup-face 1a of Comparative Example 3 is shown in a plan view of
The cup-face 1a of Comparative Example 2 is shown in a plan view of
The specifications and evaluation results of the individual examples are listed in Table 1 and Table 2 as below.
Description is made on the individual items in the tables.
The “number of ribs” means the number of ribs extended from the face center toward the face circumferences.
The “face backside view” means the number of the figure showing the face backside of each example in plan.
The definitions of θ1 to θ6 and R1 to R6 are as shown in
The “mean sectional area of other rib (mm2)” means the mean value of the cross-sectional areas of each of the other ribs than the upward rib, the ribs being extended from the face center toward the face circumferences.
Next, description is made on the “area of high restitution area (mm2)”.
In a contour plot of restitution coefficient distribution produced by a predetermined method, the high restitution area means the area on the face surface that has a restitution coefficient of 0.84 or more.
The contour plot of restitution coefficient distribution was produced as follows. First, a grid with the sweet spot on the face surface located at its center was formed by drawing straight lines in the head vertical direction and the toe-heel direction (perpendicular to the head vertical direction as seen on the face surface) at 5 mm-intervals. The restitution coefficient of the head was measured at each of the intersections thus formed (hereinafter, also referred to as “grid point”). A measurement range was defined as 20 mm toward the toe side and 20 mm toward the heel side from the sweet spot and 15 mm toward the crown side and 15 mm toward the sole side from the sweet spot with respect to the head vertical direction.
The measurements of restitution coefficient taken at the individual grid points were applied to a statistical software (STATISTICA commercially available from StataSoft. Inc.) so as to produce the contour plot of restitution coefficient distribution showing the restitution coefficient distribution in the form of contour lines.
The “durability” was evaluated as follows. The shaft and grip were mounted to the head of each of the examples so as to fabricate a golf club. The resultant golf club was attached to a swing robot to hit 1000 balls at a head speed of 50 m/s. The robot was adjusted to hit the ball on the face center as the ball impact point. The face surfaces of the heads were examined for dents produced by the impact with the balls. A head sustaining a dent of a depth of 0.1 mm or less was rated as ◯, whereas a head sustaining a dent of a depth of more than 0.1 mm was rated as Δ. A head sustaining face surface fracture before 1000 balls were hit was rated as X.
When the aforementioned contour plot of restitution coefficient distribution was produced, the restitution coefficients at the respective grid points were determined based on a method analogous to the Procedure for Measuring the Velocity Ratio of a Club Head for Conformance to Rule 4-1e, Revision 2 (Feb. 8, 1999) specified by USGA. Specifically, a golf ball was shot by means of a ball shooting machine so as to strike on the face portion of the head at place near the aforesaid grid point, the head being unfixedly placed on a base. The restitution coefficient at each grid point was determined as follows. The ball was shot square on the face surface at place 5 mm or less from the grid point on the head. The measurement was taken on the incident velocity Vi of the golf ball just before impact and on the bounce-back velocity Vo thereof. Provided that Vi represents the incident velocity of the golf ball, Vo represents the bounce-back velocity thereof, M represents the head mass and m represents the mean mass thereof, the restitution coefficient e at each grid point was calculated based on the following equation:
(Vo/Vi)=(eM−m)/(M+m)
Incidentally, a distance between a golf-ball shooting aperture and the face portion was defined as 1 m. The golf balls used in the measurement were Pinacle Gold Series commercially available from Titleit Inc. The initial ball velocity was set to 48.77 m/s. Further, the velocity sensors were positioned at places 360.2 mm from the head, respectively.
According to the comprehensive evaluation of the areas of high-restitution areas (percentages) and the durability, the examples of the invention achieved the better results than the comparative examples, as shown in the tables.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-337844 | Nov 2004 | JP | national |
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| Number | Date | Country | |
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| 20060111201 A1 | May 2006 | US |
