Wood-type golf club head

The present invention relates to a wood-type golf club head, more particularly to a segmented hollow structure capable of increasing the moment of inertia of the head.

In recent years, various wood-type golf club heads having large head volumes have been proposed. In general, such a large-sized club head has a large lateral moment of inertia around a vertical axis passing through the center of gravity of the head. Accordingly, even if the ball hitting position is off centered toward the toe or heel, the rotational motion of the head around the vertical axis becomes smaller, and thereby the directionality of the ball becomes stable.

On the other hand, if the ball hitting position is off centered toward the crown or sole, then due to the vertical gear effect, there is a possibility that the traveling distance of the ball is decreased.

As shown in FIG. 8, when the ball hits a position on the club face (f) above or below the sweet spot SS, a moment substantially equal to the product of an impulsive force F and the distance L1 or L2 to the center of gravity G of the head is caused on the club head (a). Due to this moment, the club head makes an angularly very small rotational motion around the horizontal axis passing through the center of gravity G parallel with the toe-heel direction. By the rotational motion of the head, the ball (b) contacting with the club face (f) is forced to make a rotational motion in the opposite direction due to the friction therebetween. Such phenomenon is called vertical gear effect.

Accordingly, in the case that the ball hitting position is above the sweet spot SS (upper hit), the backspin of the ball (b) is decreased and it becomes difficult to obtain a sufficient ballistic course height.

Contrary, in the case that the ball hitting position is under the sweet spot SS (lower hit), the backspin of the ball (b) is increased, therefore, there is a tendency that the ball rises high and receives a ballooning effect.

Thus, the carry distance is decreased in either case.

In order to stabilize the carry distance of the ball or lessen the variations of the carry distances even if the ball hitting position is off-centered upward or downward of the sweet spot, it is necessary to lessen the above-mentioned vertical gear effect. For this purpose, it is effective to decrease the above-mentioned rotational motion by increasing the vertical moment of inertia of the head around the horizontal axis passing through the center of gravity G parallel with the toe-heel direction.

In the meantime, according to the Rules of Golf, the upper limit for the volume of a club head is provided. Therefore, if the lateral moment of inertia and vertical moment of inertia are increased under such limitation, the mass of the club head is excessively increased, and problems arise such as a decrease in the head speed and deterioration of the swing balance.

It is therefore, an object of the present invention to provide a wood-type golf club head, in which variations of the carry distances between good shots and missed shots can be decreased without a substantial increase in the mass of the head.

According to the present invention, a wood-type hollow golf club head has a ratio (Mb/Ma) of the vertical moment of inertia Mb to the lateral moment of inertia Ma which is not less than 0.80.