preferred embodiments of the present invention will now be described in detail with reference to the attached fig1 to 4 , 7 and 8 . fig1 to 3 show a metal golf club head according to the first embodiment of the present invention . the head includes a hollow shell 17 made from a material such as stainless steel , titanium , aluminum alloy , iron or fiber reinforced metallic composites . the shell 17 is formed by a cup portion 21 ( including sole portion 23 , hosel portion 25 and top portion 27 ), an opening portion 33 , and a bottom 19 . the inner chamber 29 of the shell 17 is filled with a filling member 31 such as synthetic resin foam . the opening portion 33 receives a face plate 35 made of metal , synthetic resin , ceramics , fiber reinforced resin , etc . which is secured to the bottom 19 with adhesive and / or screw ( s ) 37 as shown in fig3 . the end ( s ) of screw ( s ) 37 are flush with a ball hitting surface on the face plate 35 . the components of the shell 17 ( cup portion 21 , opening portion 33 and bottom 19 ) are either integrally formed or subsequently joined such that the cup portion 21 and the opening portion 33 share a first con , non perimeter 33a . similarly , the bottom 19 and the opening portion 33 share a second common perimeter 33b . the opening portion 33 extends from the first common perimeter 33a into the interior of the cup portion 21 , thereby creating a v - shape with the first con , non perimeter 33a at the apex . further , the first common perimeter 33a is also relatively larger than the second common perimeter 33b . as illustrated with two - dotted chain line in fig3 when the face plate 35 hits a golf ball 39 , the bottom 19 is elastically deformed into the cup portion 21 due to the impact with the golf ball 39 , thereby storing potential energy . potential energy is also stored during the associated elastic deformation of the opening portion 33 and the cup portion 21 . as shown in fig2 the thickness of the face plate 35 is increased near a &# 34 ; sweet &# 34 ; spot 35c relative to its toe side 35a and heel side 35b , thereby defining a curved ball hitting surface . the curved ball hitting surface enhances a gear effect between the ball 39 and ball hitting surface when the golf ball is hit . that is to say , when golf ball 39 is not hit with the sweet spot 35c , the curved ball hitting surface functions to drive the ball near the intended orbit . the face plate 35 may also be made of woven fabric reinforced synthetic resin which provides excellent elastic energy transmission characteristics between the hollow shell 17 and the ball 39 as compared with the other materials mentioned previously . the bottom 19 , the opening portion 33 , the sole portion 23 and the top portion 27 of the hollow shell 17 have substantially the same wall thickness . however , wall thickness may be reduced nearer to a back portion 41 of the cup portion 21 so as to more readily store potential energy from the diminished deformation forces received at the back portion 41 . consequently , potential energy is stored in the entire shell 17 . when a golf ball 39 is hit with the golf club according to the present invention as described above , the bottom 19 is elastically deformed into the cup portion 21 and the opening portion 33 is also elastically deformed as shown by two - dotted line in fig3 so that the impact transmitted through the face plate 35 is stored as potential energy the hollow shell 17 . further , the sole portion 23 and the top portion 27 are also elastically deformed , as is the reduced thickness back portion 41 of the cup portion 21 , so that the impact of the golf club head hitting the golf ball 39 is stored as potential energy throughout the entire shell 17 . subsequently , all of the potential energy is transmitted back to the golf ball 39 so as to drive the golf ball 39 further . moreover , since the bottom 19 and opening portion 33 are simultaneously deformed , and the sole portion 23 and top portion 27 are also elastically deformed , as is the reduced thickness back portion 41 of the cup portion 21 , the deformation absorbs the impact so as to provide a &# 34 ; soft &# 34 ; feeling when hitting the golf ball 39 , as well as minimize stress concentration which could otherwise damage or brake the bottom 19 . therefore , the golf club head according to the present invention is more durable with respect to the impact caused when hitting a golf ball , enhances driving performance in comparison with the prior art shown in fig5 and 6 , and provides a &# 34 ; soft &# 34 ; feeling when hitting a golf ball due the deformation and potential energy stored throughout the entire shell 17 . fig4 a to 4c show a golf club head according to the second embodiment of the present invention including a concave portion 49 , which may be semi - cylindrical ( fig4 a and 4b ) or parabolic ( fig4 c and 4d ), in place of the opening portion 33 and the bottom 19 of the first embodiment . unless otherwise noted , reference numerals common to both the first and the second embodiments denote equivalent parts . in fig4 a to 4c , reference numeral 43 designates a hollow shell ( in place of the hollow shell 17 in the first embodiment ) formed by the cup portion 21 , the sole portion 23 , the hosel portion 25 , the top portion 27 and the concave portion 49 , all of which are made of the same material . an inner chamber 47 of the hollow shell 43 is filled with a filling member 31 . the cup portion 21 may also have reduced wall thickness in the proximity of back portion 41 , as discussed previously . the components of the shell 43 ( cup portion 21 and concave portion 49 ) are either integrally formed or subsequently joined such that the cup portion 21 and the concave portion 49 share a first perimeter 49a . a face plate 51 having a curved golf ball hitting surface similar to the face plate 35 in the first embodiment , is mounted and secured to the concave portion 49 with adhesive and / or screw ( s ), as described above . when a golf ball 39 is hit with the golf club head according to the second embodiment , the concave portion 49 is elastically deformed into the interior of the cup portion 21 . the impact with the golf ball 39 is transmitted through the face plate 51 to the hollow shell 43 , storing potential energy . the sole portion 23 and rod portion 27 of the outer shell 43 are also deformed , as is the reduced thickness back portion 41 , so that potential energy is stored throughout the outer shell 43 . subsequently , the potential energy is transmitted back to the golf ball 39 to drive the golf ball 39 further . further , since the distance between the correct ball hitting point and the concave portion 49 is uniform by virtue of the semi - circular cross - sectional shape , the stored potential energy can be efficiently transmitted back to the golf ball 39 . moreover , since the concave portion 49 , the sole portion 23 and top portion 27 are elastically deformed , as is the reduced thickness back portion 41 of the cup portion 21 , the deformation absorbs the impact to provide a &# 34 ; soft &# 34 ; feeling when hitting the golf ball 39 , as well as minimize stress concentration which could otherwise damage or brake the concave portion 49 . therefore , the golf club head according to the second embodiment of present invention is also more durable with respect to the impact caused when hitting a golf ball , also enhances driving performance in comparison with the prior art shown in fig5 and 6 , and also provides a &# 34 ; soft &# 34 ; feeling when hitting a golf ball due the deformation and potential energy stored throughout the entire shell 43 . fig7 and 8 show a golf club head according to the third embodiment of the present invention . a hollow shell 117 is formed by the cup portion 21 , including the sole portion 23 , the hosel portion 25 and the top portion 27 , as similarly described with respect to the first and second embodiments , and a bottom 119 located inside the cup portion 21 . the bottom 119 and the cup portion 21 share a common perimeter 119a which is larger than perimeter 117a of the opening of the cup portion . a face plate 135 is forcibly inserted into the recess bounded between the opening perimeter 117a and the bottom 119 , or the face plate 135 may be molded in situ with a curved ball hitting surface . in the third embodiment , the bottom 119 may be either planar or have a curved surface to minimize stress concentration when hitting the golf ball 39 . the curved bottom 119 and the reduced wall thickness at the back portion 41 enable the entire hollow shell 117 to be elastically deformed and efficiently store and transmit potential energy due to the impact with the golf ball 39 . an inner chamber 129 of the hollow shell 117 is similarly filled with the filling member 31 . further , since the opening perimeter 117a is smaller than the common perimeter 119a , the face plate 135 is securely fixed to the hollow shell 117 without adhesives or screws , regardless of the vibration of the golf club head . the hollow shell 17 , 43 , 117 may also remain hollow without filling the inner chamber with the filling member 31 , and still provide the desired effect .
a golf club head which is more durable , capable of driving a golf ball further and providing a desirable , &# 34 ; soft &# 34 ; feeling when hitting the golf ball . these objectives are achieved by configuring the head to efficiently transmit and store potential energy due to impact with the golf ball . the head comprises a hollow shell defining a cup portion and an opening or concave portion which receives a face plate . the face plate forms a contact surface for striking a golf ball . the structural arrangement causes the hollow shell to elastically deform upon contact with a golf ball to enhance driving performance .