There are today many golf clubs, or to be more precise, golf club heads of the type mentioned above. What characterises these known club heads is that they have a flat or rounded shaped sole. These club heads have a bottom sur- face or sole shape that results in relatively large areas being exposed to the ground during the strike. This will obviously result in great friction resistance be- tween the club's sole and the ground, which again results in part of the force of the strike being lost in the form of friction against the ground.

One object of the present invention is therefore to eliminate or at least re- duce this loss in friction as much as possible, so that as much force as possible is transferred to the golf ball, thus increasing the length of the strike correspond- ingly.

Another object of the present invention is that a player should be able to achieve best possible control during the performance of a hit under varying con- ditions. I. e. that the golf club head must be turned as little as possible, when the head hits the ball. This will result in the golf ball achieving a more optimal trajec- tory.

The present invention shall solve these problems associated with the known golf club heads, and furthermore achieve amongst others the objects de- scribed above.

This is achieved according to the invention by a golf club head as men- tioned in the introduction of the description and that is recognised by that the bot- tom surface within a centre area is arranged with a recess in the shape of an cu- ved lowered area that increases evenly in depth from an area inside the back edge of the bottom surface and towards the front edge of the bottom surface.

The preferred embodiments of the invention are described more thor- oughly in the claims 2 to 6.

The embodiments of the golf club head according to the present invention will now be explained with reference to figures, wherein

Figure 1 shows a golf club head according to the present invention show- ing the hitting surface and with the shaft connection pointing upwards and to the right, Figure 2 shows the golf club head in Figure 1 seen from the back area and with the shaft connection pointing downwards and to the right, Figure 3 shows a schematic diagram of the bottom surface of the club head in Figure 2, Figure 4 shows a cross section through section X-X in Figure 3, Figure 5 shows a first embodiment of the club head according to the pre- sent invention, Figure 6 shows a second embodiment of the club head according to the present invention, and Figure 7 shows a third embodiment of the golf club head according to the present invention.

Referring first to Figure 1, a front area or a hitting surface 2 of a golf club head 1 is shown. The golf club head 1 has a mainly flat hitting surface 2 and is further arranged with a shaft connection 3 pointing to the right hand in the Figure.

Figure 2 shows a back area 5 of the golf club head 1 in Figure 1. The shaft con- nection 3 is here shown pointing downwards to the right. The golf club head 1 has furthermore a bottom surface or sole 6 and a side surface 4. The bottom sur- face 6 and the side surface 4 are rounded. The bottom surface 6 is further ar- ranged with a grove in the shape of a rounded lowered area 9. The lowered area 9 is arranged in a centre area of the bottom surface 6 that will be below the hit- ting surface's hitting point on the ball. The lowered area 9 has an evenly increas- ing depth from an area 10 inside the bottom surface's back edge 8 and towards the bottom area's front edge 7. The bottom area's front edge 7, seen from the front towards the hitting surface in Figure 1, will however not include this lowered area 9. The grove starts just inside the bottom surface's front edge 7. This is shown more clearly in Figure 4 where the lowered area 9 stretches from an area 10 inside the bottom surface's back edge 8 and finishes inside the bottom sur- face's front edge 7. The lowered area 9 will have a maximum depth D against the front edge 7. Depth D will vary depending on the club head's application and de- sign, which will be explained later in the description. The depth will normally lie in the range 0.5 to 2.5 mm. The lowered area 9 has moreover an even, rounded

and concave curvature. The area of the lowered part 9 can be described as a circle or elliptical shaped sector having approximate diameter C along and inside the bottom surface's front edge 7 and with height B from the grove's finish at the front edge 7 and to the area 10 inside the bottom surface's back edge 8. Diame- ter C will vary from 10 to 50 mm depending on the club head type as mentioned above. Height B of the lowered area will vary from 0.5 to 30 mm depending on the club type. Figure 3 shows the lowered area 9 in the bottom surface 6 with specification of the diameter C and the height B.

The design of the club heads according to the present invention will vary, as previously mentioned, with regards to the application. For golf club heads of type"Iron and Wedges"the club head's shape, weight etc. will depend on the classification in accordance with the following numbering system which is stan- dard in the field in question: #1, #2, #3, #4, #5, #6, #7, #8, #9, #SW, LP, PW, AW.

Figures 5 and 6 show the principles of the present invention applied to club heads of"Iron-"type and more precisely of the"Classic-"type and"Tour-" type, respectively. Figure 7 shows the principles applied to a club head of the "Wedge-"type. It should be noted that in Figures 5,6 and 7 the same reference numbers for the same parts are used as in the preceding drawings 1 to 4, inclu- sive.

The inventor of the present invention has, during the development of the golf club head, carried out extensive studies, for example, with regards to the time the ball is in contact with the club head. Depending on the type of golf club head, as described earlier, this contact time will normally vary from 0.4 to 2.0 ms.

The shape of the club head according to the present invention, especially with regards to the grove in the sole, will give soil and grass the possibility to"settle" or disappear in the mentioned milliseconds during ball contact and before the club head starts to dig itself into the ground. Due to the special sole shape, the club head will give the player better stability during the performance of a hit, re- duce the club head's turning and create a more optimal ball trajectory. Hits that have initially more or less failed, will, with the invented club head, still possibly give a satisfactory result. The club head shape according to the present invention will help raise the ball quickly with"Long Irons", and give the ball a more forceful trajectory with"Low Irons". The result is that the golf club heads according to the present invention will give the player significantly better control during the per- formance of a hit, and thus a significantly improved result will be achieved, com- pared to what would be achieved with existing golf club heads of this type.