Patent Publication Number: US-10758792-B2

Title: Iron type golf club head

Description:
The present application claims priority on Patent Application No. 2018-009400 filed in JAPAN on Jan. 24, 2018. The entire contents of this Japanese Patent Application are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an iron type golf club head. 
     Description of the Related Art 
     As iron type golf club heads, a flat back iron and a cavity back iron have been known. 
     JP8-774A discloses an iron head that has almost the same center-of-gravity distance as that of an ordinary flat back iron, and that has the same moment of inertia as that of an ordinary cavity back iron. 
     SUMMARY OF THE INVENTION 
     The present inventor has found that there is room to improve a conventional iron type golf club head. 
     It is an object of the present disclosure to provide an iron type golf club head having an excellent hit feeling and capable of suppressing variations in flight distances. 
     In one aspect, an iron type golf club head includes a face surface, a back surface, a sole surface, and a top blade. The back surface includes a top-side region and a sole-side region located between the top-side region and the sole surface. The top-side region includes: a toe recess part located on a toe side relative to a face center; a heel recess part located on a heel side relative to the face center; and a first thick portion extending along the top blade, located on an upper side of the toe recess part, and located on an upper side of the heel recess part. In a reference state in which the head is placed on a horizontal plane, an angle between a lower edge of the first thick portion and the horizontal plane is denoted by θ1, and an angle between the top blade and the horizontal plane is denoted by θ2. The angle θ1 is smaller than the angle θ2. 
     In another aspect, a second thick portion may be formed between the toe recess part and the heel recess part. The second thick portion may be located in a region that includes a sweet spot. 
     In another aspect, the toe recess part may reach a toe-side edge of the head, and a side recess part may be formed on a toe side surface of the head by the reaching of the toe recess part. The side recess part may be invisible when the head in the reference state is viewed from a reference viewpoint located vertically above the head. 
     In another aspect, the toe recess part may include a toe upper-side surface formed along a lower edge of the first thick portion. The toe upper-side surface may include a toe upper inclined surface that is inclined so as to approach the face surface as going to a lower side. 
     In another aspect, a center recess part may be formed between the toe recess part and the heel recess part. The toe recess part, the heel recess part, and the center recess part may be continuous with each other to form a continuous recess part that extends from the toe side to the heel side. 
     In another aspect, a head thickness of the first thick portion is denoted by Tc1 (mm), a minimum value of a head thickness of the toe recess part is denoted by Tc3 (mm), and a minimum value of a head thickness of the heel recess part is denoted by Tc4 (mm). A difference [Tc1−Tc3] may be greater than or equal to 2.0 mm. A difference [Tc1−Tc4] may be greater than or equal to 2.0 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an iron set including a head according to a first embodiment; 
         FIG. 2  is a front view of the head according to the first embodiment, as viewed from the front of a face; 
         FIG. 3A  and  FIG. 3B  are back views of the head in  FIG. 2 , and  FIG. 3A  is a shaded view; 
         FIG. 4  is a perspective view of the head in  FIG. 2 , and  FIG. 4  is a shaded view; 
         FIG. 5  is a side view of the head in  FIG. 2  as viewed from a toe side, and  FIG. 5  is a shaded view; 
         FIG. 6  is a sectional view taken along line A-A of  FIG. 2 ; 
         FIG. 7  is a sectional view taken along line B-B of  FIG. 2 ; 
         FIG. 8  is a sectional view taken along line C-C of  FIG. 2 ; 
         FIG. 9  is a plan view of the head in  FIG. 2  as viewed from above; 
         FIG. 10  is a diagram illustrating a reference viewpoint; 
         FIG. 11  is a back view of a head according to a second embodiment; 
         FIG. 12  is a back view of a head according to a third embodiment; and 
         FIG. 13  is a diagram illustrating a reference state. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with appropriate references to the accompanying drawings. 
     Definitions of Terms 
     Terms appeared in the present application are defined as follows. 
     [Reference State] 
     The reference state is a state where a head is placed on a horizontal plane HP in a state where the horizontal plane HP and a face line gv are parallel to each other. In the reference state, a center axis line Z (shaft axis line Z) of a shaft hole of the head is disposed in a reference perpendicular plane VP (see  FIG. 13 ). The reference perpendicular plane VP is a plane perpendicular to the horizontal plane HP. In the reference state, the face line gv is parallel to the horizontal plane HP, and parallel to the reference perpendicular plane VP. 
     [Toe-Heel Direction] 
     In the head of the reference state, the direction of an intersectional line between the reference perpendicular plane VP and the horizontal plane HP is the toe-heel direction (see  FIG. 13 ). The toe-heel direction is parallel to the face line gv. 
     [Face-Back Direction] 
     A direction perpendicular to the toe-heel direction and parallel to the horizontal plane HP is the face-back direction (see  FIG. 13 ). The face-back direction is also a front-rear direction. A face side is also referred to as a front side. 
     [Up-Down Direction] 
     A direction perpendicular to the toe-heel direction and perpendicular to the face-back direction is the up-down direction. 
     [Middle Position Pc of Face Line] 
     The middle position of a longest face line gv 1  in the toe-heel direction is a middle position Pc of the face line (see  FIG. 2  to be described later). The middle position Pc is a position in the toe-heel direction. When a plurality of longest face lines gv 1  are present, the middle position Pc is determined based on the lowermost longest face line gv 1 . 
     [Face Center Fc] 
     On the middle position Pc of the face line, a center of the up-down direction width of the face is determined. The center is the face center Fc (see  FIG. 2  to be described later). 
     [Toe Reference Position Pt] 
     The position of a toe-side end of the longest face line gv 1  is a toe reference position Pt (see  FIG. 2  to be described later). The toe reference position Pt is a position in the toe-heel direction. When the plurality of longest face lines gv 1  are present, the toe reference position Pt is determined based on the lowermost longest face line gv 1 . 
     [Heel Reference Position Ph] 
     The position of a heel-side end of the longest face line gv 1  is a heel reference position Ph (see  FIG. 2  to be described later). The heel reference position Ph is a position in the toe-heel direction. When the plurality of longest face lines gv 1  are present, the heel reference position Ph is determined based on the lowermost longest face line gv 1 . 
     [Sweet Spot SS] 
     The sweet spot SS is an intersection point between the face surface and a straight line passing through a center of gravity of the head and perpendicular to the face surface. 
       FIG. 1  shows a golf club set  2  according to a first embodiment. The set  2  includes a plurality of golf clubs  4 . In the present embodiment, the set  2  includes seven golf clubs  4 . The set  2  includes a first golf club  41 , a second golf club  42 , a third golf club  43 , a fourth golf club  44 , a fifth golf club  45 , a sixth golf club  46 , and a seventh golf club  47 . 
     The set  2  includes the plurality of golf clubs  4  having different loft angles. In the set  2 , the club length is decreased as the loft angle is increased. The loft angle means a real loft angle. The real loft angle means a loft angle with respect to the shaft axis line. 
     The number of the clubs of the set  2  is greater than or equal to 2. In the set  2 , the number of the clubs is 7. Advantageous effects to be described later are effective in all the club numbers. In this respect, the number of the clubs of the set  2  is preferably greater than or equal to 3, more preferably greater than or equal to 4, and still more preferably greater than or equal to 5. In the golf rules, the number of clubs capable of being used during play is limited. In this respect, the number of the clubs of the set  2  is preferably less than or equal to 10, more preferably less than or equal to 9, and still more preferably less than or equal to 8. 
     Each of the golf clubs  4  includes a head  6 , a shaft  8 , and a grip  10 . The first golf club  41  includes a head  61 , a shaft  81 , and a grip  10 . The second golf club  42  includes a head  62 , a shaft  82 , and a grip  10 . The third golf club  43  includes a head  63 , a shaft  83 , and a grip  10 . The fourth golf club  44  includes a head  64 , a shaft  84 , and a grip  10 . The fifth golf club  45  includes a head  65 , a shaft  85 , and a grip  10 . The sixth golf club  46  includes a head  66 , a shaft  86 , and a grip  10 . The seventh golf club  47  includes a head  67 , a shaft  87 , and a grip  10 . In the set  2 , the length of the shaft  8  is changed in accordance with club length. The grips  10  of all the club numbers are the same. 
     The first golf club  41  is a 4-iron. The second golf club  42  is a 5-iron. The third golf club  43  is a 6-iron. The fourth golf club  44  is a 7-iron. The fifth golf club  45  is an 8-iron. The sixth golf club  46  is a 9-iron. The seventh golf club  47  is a pitching wedge. These club numbers are shown as merely an example. The club number of the head  6  is not limited. Note that the present invention is directed to a single head, and thus needs not be a set. 
     Hereinafter, the head  6  (head  61 ) of the 4-iron is shown as an example. However, the following description applies to all the head  6  (heads  61  to  67 ). 
       FIG. 2  is a front view of the head  6  as viewed from a direction perpendicular to a face surface thereof.  FIG. 3A  is a shaded view showing a back surface of the head  6 . In  FIG. 3A , unevenness is shown by shading.  FIG. 3B  is a back view of the head  6 . The unevenness of the back surface of the head  6  is hard to depict only by a line drawing such as  FIG. 3B . For this reason,  FIG. 3A  is shown in addition to a usual drawing ( FIG. 3B ).  FIG. 4  is a perspective view of the head  6  as viewed from an obliquely rear side, and  FIG. 5  is a side view of the head  6  as viewed from the toe side. These  FIG. 4  and  FIG. 5  are also shaded views. 
     As shown in  FIG. 2  to  FIG. 5 , the head  6  includes a face surface  14 , aback surface  16 , a sole surface  18 , and a top blade  20 . The head  6  further includes a hosel  22 . The hosel  22  includes a shaft hole  24 . 
     The face surface  14  includes a plurality of face lines gv. The face lines gv include a longest face line gv 1 . The longest face line gv in the plurality of face lines gv is the longest face line gv 1 . 
     If the face lines gv are disregarded, the face surface  14  is a plane. Therefore, in the present application, the face surface  14  is treated as a plane. 
     The description of the face lines gv is omitted except for  FIG. 2 . 
     As described above, the middle position Pc of the face line, the toe reference position Pt and the heel reference position Ph are defined based on the longest face line gv 1  (see  FIG. 2 ). 
     The face surface  14  includes the face center Fc. As described above, the face center Fc is the center of the up-down direction width of the face surface  14  in the middle position Pc of the face line. 
     The face surface  14  includes the sweet spot SS. In the present embodiment, the sweet pot SS is located on the heel side relative to the face center Fc. In the present embodiment, the sweet spot SS is located on the lower side relative to the face center Fc. 
     The face surface  14  is a hitting face. A ball collides against the face surface  14  at impact. 
     The back surface  16  is a surface opposite to the face surface  14 . The back surface  16  is also referred to as a back face. 
     The sole surface  18  constitutes a lower surface of the head  6 . The sole surface  18  is located on the lower side of the face surface  14 . The sole surface  18  is located on the lower side of the back surface  16 . The sole surface  18  extends between a lower edge of the face surface  14  and a lower edge of the back surface  16 . 
     The top blade  20  constitutes an upper surface of the head  6 . The top blade  20  is located on the upper side of the face surface  14 . The top blade  20  is located on the upper side of the back surface  16 . The top blade  20  extends between an upper edge of the face surface  14  and an upper edge of the back surface  16 . 
     The back surface  16  includes a top-side region B 1  and a sole-side region B 2 . The top-side region B 1  is located on the upper side of the sole-side region B 2 . The top-side region B 1  is located between the sole-side region B 2  and the top blade  20 . The sole-side region B 2  is located on the lower side of the top-side region B 1 . The sole-side region B 2  is located between the top-side region B 1  and the sole surface  18 . 
     In the head  6 , a head lower portion that is continuous with the sole has a large thickness. The head lower portion is included in the sole-side region B 2 . On the other hand, a head upper portion that is located on the upper side relative to the head lower portion has a small thickness as compared with the head lower portion. The head upper portion is included in the top-side region B 1 . 
     A boundary between the top-side region B 1  and the sole-side region B 2  may be determined based on head thickness. For example, a location (a contour line) having a head thickness of 7.0 mm may be the boundary between the top-side region B 1  and the sole-side region B 2 . The sole-side region B 2  includes a portion having a head thickness larger than the maximum value of the head thickness in the top-side region B 1 . When the maximum value of the head thickness in a first thick portion T 1  and a second thick portion T 2  to be described later is denoted by Tmax, a region having a head thickness larger than Tmax may be defined as the sole-side region B 2 . When the head does not include the second thick portion T 2 , the maximum value of the head thickness in the first thick portion T 1  can be Tmax. 
     The maximum value of the head thickness in the sole-side region B 2  is preferably greater than or equal to 10 mm, more preferably greater than or equal to 13 mm, and still more preferably greater than or equal to 15 mm. In view of restriction on head weight, the maximum value of the head thickness in the sole-side region B 2  is preferably less than or equal to 25 mm. 
     In the present application, “thickness” means the head thickness. The thickness is measured along a direction perpendicular to the face surface  14 . 
     In general, the type of the back surface of an iron head is broadly classified into a cavity back or a flat back. The cavity back might be further classified into an undercut cavity (pocket cavity) or the remainder. The flat back is also referred to as a muscle back. 
     The back surface  16  of the head  6  is not the cavity back. The back surface  16  of the head  6  is the flat back. In other words, the back surface  16  of the head  6  is the muscle back. Note that the “flat back” means that the back surface is similar to a plane as compared to the cavity back, and does not mean that the whole back surface is flat. 
     In general, the definition of the cavity back iron is not necessarily clear. In this respect, the present invention does not exclude the cavity back iron. 
     A typical cavity back iron includes the following structure (a). The head  6 , however, does not include the structure (a). 
     (a) A cavity is provided on the back surface; the cavity is located in a region including the sweet spot SS; and the whole circumference of the cavity is surrounded by a thick portion having a head thickness greater than that of the cavity. 
     A typical cavity back iron includes the following structure (b). The head  6  according to the present embodiment, however, does not include the structure (b). 
     (b) A cavity is provided on the back surface; the bottom surface of the cavity is formed by a constant thickness portion in which the head thickness is constant; and the constant thickness portion has an area of greater than or equal to 500 mm 2 . 
     A typical cavity back includes the following structure (c). The head  6 , however, does not include the structure (c). 
     (c) A cavity is provided on the back surface; the bottom surface of the cavity is formed by a constant thickness portion in which the head thickness is constant; and the constant thickness portion is located in a region including the sweet spot SS and the face center Fc. 
     A typical cavity back includes the following structure (d). The head  6 , however, does not include the structure (d). 
     (d) In the above structure (b), the head thickness of the constant thickness portion is greater than or equal to 1.5 mm and less than or equal to 3 mm. 
     A typical cavity back includes the following structure (e). The head  6 , however, does not include the structure (e). 
     (e) In the above structure (c), the head thickness of the constant thickness portion is greater than or equal to 1.5 mm and less than or equal to 3 mm. 
     As shown in  FIG. 3A  and  FIG. 3B , the top-side region B 1  (back surface  16 ) includes a toe recess part Rt and a heel recess part Rh. 
     The toe recess part Rt is located on the toe side relative to the face center Fc. The toe recess part Rt is located in a region including the toe reference position Pt. The toe recess part Rt is located in a region that does not include the heel reference position Ph. 
     The toe recess part Rt reaches a toe-side edge of the head  6  (back surface  16 ). In other words, a toe-side edge of the toe recess part Rt constitutes a part of the edge of the head  6 . As shown in  FIG. 5 , the side surface of the head  6  is narrowed in the portion to which the toe recess part Rt reaches. The toe recess part Rt reaches the toe-side edge of the head  6 , thereby forming a side recess part S 1  on the toe side surface of the head  6 . The side recess part S 1  is a portion in which the toe side surface of the head  6  is partially narrowed (see  FIG. 5 ). 
     The heel recess part Rh is located on the heel side relative to the face center Fc. The heel recess part Rh is located in a region including the heel reference position Ph. The heel recess part Rh is located in a region that does not include the toe reference position Pt. 
     The heel recess part Rh reaches a heel-side edge of the back surface  16 . In other words, a heel-side edge of the heel recess part Rh constitutes a part of the edge of the back surface  16 . 
     As shown in  FIG. 3A  and  FIG. 3B , the top-side region B 1  (back surface  16 ) includes the first thick portion T 1 . The first thick portion T 1  extends along the top blade  20 . The first thick portion T 1  is adjacent to the top blade  20 . The upper edge of the first thick portion T 1  is the top blade  20 . 
     A part of the first thick portion T 1  is located on the upper side of the toe recess part Rt. The toe recess part Rt is located between the first thick portion T 1  and the sole-side region B 2 . The head thickness of the first thick portion T 1  is greater than the head thickness of the toe recess part Rt. 
     A part of the first thick portion T 1  is located on the upper side of the heel recess part Rh. The heel recess part Rh is located between the first thick portion T 1  and the sole-side region B 2 . The head thickness of the first thick portion T 1  is greater than the head thickness of the heel recess part Rh. 
     As shown in  FIG. 3A  and  FIG. 3B , the top-side region B 1  (back surface  16 ) includes the second thick portion T 2 . The second thick portion T 2  is located on the toe side relative to the heel recess part Rh. The second thick portion T 2  is located on the heel side relative to the toe recess part Rt. The second thick portion T 2  is formed between the toe recess part Rt and the heel recess part Rh. 
     The second thick portion T 2  is located in a region including the sweet spot SS (see  FIG. 2 ). In other words, a straight line passing through the center of gravity of the head and perpendicular to the face surface  14  passes through the second thick portion T 2 . 
     The second thick portion T 2  is located in a region including the face center Fc. The second thick portion T 2  is located in a region that does not include the toe reference position Pt. The second thick portion T 2  is located in a region that does not include the heel reference position Ph. 
     The head thickness of the second thick portion T 2  is greater than the head thickness of the toe recess part Rt. The head thickness of the second thick portion T 2  is greater than the head thickness of the heel recess part Rh. 
     As shown in  FIG. 3A  and  FIG. 3B , the second thick portion T 2  includes a width changing portion T 21  that has a width increasing toward the sole surface  18 . In the head  6 , the whole second thick portion T 2  is the width changing portion T 21 . A part of the second thick portion T 2  may be the width changing portion T 21 . 
     As shown in  FIG. 3A  and  FIG. 3B , the first thick portion T 1  and the second thick portion T 2  are continuous with each other without a step. 
     In  FIG. 3B , an angle θ1 and an angle θ2 are shown. In the reference state, an angle between the lower edge of the first thick portion T 1  and the horizontal plane HP is denoted by θ1. The angle θ1 is an angle formed by a straight line L 1  extending along the lower edge of the first thick portion T 1  and the horizontal plane HP. In the reference state, an angle between the top blade  20  and the horizontal plane HP is denoted by θ2. The angle θ2 is an angle formed by a straight line L 2  extending along the top blade  20  and the horizontal plane HP. In the head  6 , the angle θ1 is smaller than the angle θ2. 
     When the lower edge of the first thick portion T 1  is formed along a curved line, the straight line L 1  is a tangent line of the curved line. In this case, the direction of the straight line L 1  is changed depending on the point of contact, whereby the angle θ1 is also changed. Therefore, in this case, the angle θ1 has a maximum value θ1max and a minimum value θ1min. When the top blade  20  is formed along a curved line, the straight line L 2  is a tangent line of the curved line. In this case, the direction of the straight line L 2  is changed depending on the point of contact, whereby the angle θ2 is also changed. Therefore, in this case, the angle θ2 has a maximum value θ2max and a minimum value θ2min. Preferably, θ1max is smaller than θ2min. In the present application, “θ1&lt;θ2” can mean “θ1max&lt;θ2 min”. 
     As shown in  FIG. 3A  and  FIG. 3B , the first thick portion T 1  has an up-down direction width that increases toward the toe side. A weight distributed to the first thick portion T 1  is increased by the increased up-down direction width. 
       FIG. 6  is a sectional view taken along line A-A in  FIG. 2 .  FIG. 6  is the sectional view of the head  6  at the toe reference position Pt.  FIG. 7  is a sectional view taken along line B-B in  FIG. 2 .  FIG. 7  is the sectional view of the head  6  at the middle position Pc of the face line.  FIG. 8  is a sectional view taken along line C-C in  FIG. 2 .  FIG. 8  is the sectional view of the head  6  at the heel reference position Ph. As shown in  FIG. 6  to  FIG. 8 , the head  6  is solid. In other words, the head  6  does not include a hollow portion. The head  6  does not include an undercut portion, either. The undercut portion in the present application means a portion in which a head section taken along a plane perpendicular to the face surface  14  and parallel to the face line gv is separated into a plurality of parts. 
     As shown in  FIG. 6 , on the toe reference position Pt, a point having the minimum head thickness in the top-side region B 1  is located on the toe recess part Rt. 
     As shown in  FIG. 7 , the head thickness of the first thick portion T 1  is equal to the head thickness of the second thick portion T 2 . The head thickness of the first thick portion T 1  may be different from the head thickness of the second thick portion. 
     As shown in  FIG. 8 , on the heel reference position Ph, a point having the minimum head thickness in the top-side region B 1  is located on the heel recess part Rh. 
     As shown in  FIG. 6  and  FIG. 8 , the weight of the head  6  is allocated to the upper side and the lower side. The weight of the head  6  is allocated to the upper side (first thick portion T 1 ) and the lower side (sole-side region B 2 ) of the toe recess part Rt (see  FIG. 6 ). The weight of the head  6  is allocated to the upper side (first thick portion T 1 ) and the lower side (sole-side region B 2 ) of the heel recess part Rh (see  FIG. 8 ). 
     As shown in  FIG. 3A  and  FIG. 3B , the toe recess part Rt includes a toe upper-side surface Rt 1 , a bottom surface Rt 2 , and a toe lateral inclined surface Rt 3 . The bottom surface Rt 2  is a plane. The bottom surface Rt 2  is parallel to the face surface  14 . 
     The toe upper-side surface Rt 1  is formed along the lower edge of the first thick portion T 1 . The toe upper-side surface Rt 1  connects the bottom surface Rt 2  and the first thick portion T 1 . The toe upper-side surface Rt 1  forms a thickness transition part that has a gradually changing head thickness. The toe lateral inclined surface Rt 3  connects the bottom surface Rt 2  and the second thick portion T 2 . The toe lateral inclined surface Rt 3  forms a thickness transition part that has a gradually changing head thickness. 
     The toe lateral inclined surface Rt 3  is located on the toe side of the second thick portion T 2 . The toe lateral inclined surface Rt 3  is adjacent to the second thick portion T 2 . The toe lateral inclined surface Rt 3  is inclined so as to approach the face surface  14  as going to the toe side. 
     As well shown in  FIG. 6 , the toe upper-side surface Rt 1  includes a toe upper inclined surface Rt 11  inclined so as to approach the face surface  14  as going to the lower side. In the present embodiment, the whole toe upper-side surface Rt 1  is the toe upper inclined surface Rt 11 . A part of the toe upper-side surface Rt 1  may be the toe upper inclined surface Rt 11 . 
     As shown in  FIG. 3A  and  FIG. 3B , the heel recess part Rh includes a heel upper-side surface Rh 1 , a bottom surface Rh 2 , and a heel lateral inclined surface Rh 3 . 
     The heel upper-side surface Rh 1  connects the bottom surface Rh 2  and the first thick portion T 1 . The heel upper-side surface Rh 1  forms a thickness transition part that has a gradually changing head thickness. The heel lateral inclined surface Rh 3  connects the bottom surface Rh 2  and the second thick portion T 2 . The heel lateral inclined surface Rh 3  forms a thickness transition part that has a gradually changing head thickness. 
     The heel lateral inclined surface Rh 3  is located on the heel side of the second thick portion T 2 . The heel lateral inclined surface Rh 3  is adjacent to the second thick portion T 2 . The heel lateral inclined surface Rh 3  is inclined so as to approach the face surface  14  as going to the heel side. 
     As well shown in  FIG. 8 , the heel upper-side surface Rh 1  includes a heel upper inclined surface Rh 11  inclined so as to approach the face surface  14  as going to the lower side. In the present embodiment, the whole heel upper-side surface Rh 1  is the heel upper inclined surface Rh 11 . A part of the heel upper-side surface Rh 1  may be the heel upper inclined surface Rh 11 . 
       FIG. 9  is a plan view of the head  6  in the reference state as viewed from a reference viewpoint.  FIG. 10  is a diagram for illustrating the reference viewpoint PV 1 . 
     The reference viewpoint PV 1  is a term defined in the present application. The reference viewpoint PV 1  is located vertically above the head  6  in the reference state. More specifically, the reference viewpoint PV 1  is located vertically above the face center Fc. The height Hs of the reference viewpoint PV 1  from the horizontal plane HP is set to 1.5 m. 
     In  FIG. 10 , the whole golf club  4  is depicted.  FIG. 10  shows the golf club  4  in which the head  6  is in the reference state. This position of the golf club  4  is similar to its position in the state of addressing. 
     The viewpoint of the golf player in addressing is located almost uprightly above the grip  10 . This golf player&#39;s viewpoint is located obliquely above the head  6  (upper side on the heel side). That is, the golf player&#39;s viewpoint in addressing is located obliquely above the head  6 . On the other hand, the reference viewpoint PV 1  defined in the present application is located uprightly above the head  6 . The reference viewpoint PV 1  is located on the toe side (left side in  FIG. 10 ) relative to the golf player&#39;s viewpoint in addressing. 
     The reference viewpoint PV 1  is set in order to further reliably evaluate how the toe side surface of the head  6  looks in addressing. 
     As described above, the side recess part S 1  is formed in the head  6 . Such aside recess part S 1  is not formed in a normal iron head. That is, in general, the width of the toe side surface of the head  6  in the top-side region B 1  is constant, or is changed so as to increase toward the lower side. The side recess part S 1  which is visually recognized in addressing can cause an uncomfortable feeling for golf players who are used to using such a normal head. The head  6  is likely to look to be a strange shape when the side recess part S 1  is visually recognized. 
     It is generally known that swings are strongly affected by the player&#39;s state of mind in playing golf. The strange feeling caused by how the head looks in addressing has an effect on the swing. For example, this strange feeling arouses misgivings about the orientation of the face surface  14  in addressing. The misgivings can create anxious feeling upon shots. This anxious feeling can cause disturbance in swing. The strange feeling in addressing can induce a missed shot. 
     Many of golf players who use a flat back (muscle back) iron or irons similar thereto are professional golf players or advanced-level golf players. These golf players particularly sensitive about how the head  6  looks in addressing. 
     The head  6  includes the side recess part S 1 . The side recess part S 1 , however, is invisible when the head  6  in the reference state is viewed from the reference viewpoint PV 1 . 
     As described above, the reference viewpoint PV 1  is located on the toe side relative to the golf player&#39;s viewpoint in addressing. Therefore, as compared to the golf player&#39;s viewpoint in addressing, the reference viewpoint PV 1  is located on a point from which the toe side surface of the head  6  is likely to be visible. When the side recess part S 1  is invisible from the reference viewpoint PV 1 , the side recess part S 1  is invisible from the golf player&#39;s viewpoint in addressing. 
     The reference viewpoint PV 1  is set in order to take variations in locations of golf player&#39;s viewpoint in addressing into consideration. Golf players have different heights, different arm lengths, etc. In addition, depending on the golf player, states in addressing (forward-bent angle of the player&#39;s upper half body, position of the grip, angle between the player&#39;s arm and the club, etc.) are different from each other. Because of the differences, there are variations in golf players&#39; viewpoints in addressing. In light of absorbing the variations, the reference viewpoint PV 1  is set. The reference viewpoint PV 1  is located at a point from which the toe side surface of the head  6  is more likely to be visible than when viewed from any viewpoints located within the range of the variations. Therefore, the above-mentioned visual effect is reliably brought by setting the reference viewpoint PV 1 . 
     When the head  6  in the reference state is viewed from the reference viewpoint PV 1 , at least apart of the side recess part S 1  may be visible. In this case, the toe upper inclined surface Rt 11  alleviates the above-mentioned strange feeling. As shown in  FIG. 9 , when the head  6  is viewed from above, the width of the toe side surface ST of the head  6  is gradually narrowed toward the lower side. The look of the head  6  is similar to the look of a normal head in which the width of the toe side surface ST is constant. In the head  6 , the toe upper inclined surface Rt 11  reaches the toe side surface ST. By the presence of the toe upper inclined surface Rt 11 , even if the side recess part S 1  is visible, the look of the head  6  becomes similar to the look of the normal head. Therefore, the strange feeling in addressing is reduced. Thus, when the side recess part S 1  is visible, the following structure is preferable. Of the side recess part S 1 , a portion formed by the toe upper inclined surface Rt 11  is preferably visible when the head  6  in the reference state is viewed from the reference viewpoint PV 1 . 
     Whether or not a specific portion is visible from the reference viewpoint PV 1  can be confirmed by an image viewed from the reference viewpoint PV 1 . This image can be taken by a camera. 
       FIG. 11  is a back view of a head  100  according to a second embodiment. The head  100  is the same as the head  6  except for the shape of the back surface. 
     The head  100  includes a face surface (not shown in the drawing), aback surface  116 , a sole surface  118 , and a top blade  120 . The head  100  further includes a hosel  122 . 
     The top blade  120  constitutes an upper surface of the head  100 . The top blade  120  is located on the upper side of the face surface. The top blade  120  is located on the upper side of the back surface  116 . The top blade  120  extends between an upper edge of the face surface and an upper edge of the back surface  116 . 
     The back surface  116  includes a top-side region B 1  and a sole-side region B 2 . The top-side region B 1  is located on the upper side of the sole-side region B 2 . The top-side region B 1  is located between the sole-side region B 2  and the top blade  120 . The sole-side region B 2  is located on the lower side of the top-side region B 1 . The sole-side region B 2  is located between the top-side region B 1  and the sole surface  118 . 
     The top-side region B 1  includes a toe recess part Rt and a heel recess part Rh. The top-side region B 1  further includes a center recess part Rc. The center recess part Rc is formed between the toe recess part Rt and the heel recess part Rh. Although the second thick portion T 2  is provided in the above-described head  6 , the head  100  does not includes a second thick portion T 2 . In the head  100 , the second thick portion T 2  in the head  6  is replaced with the center recess part Rc. 
     The center recess part Rc is located in a region including the sweet spot SS. The center recess part Rc is located in a region including the face center Fc. 
     The toe recess part Rt is continuous with the center recess part Rc. The center recess part Rc is continuous with the heel recess part Rh. The toe recess part Rt, the heel recess part Rh and the center recess part Rc are continuous with each other, thereby forming a continuous recess part Rx extending from the toe side to the heel side. The continuous recess part Rx continuously extends at least from the toe reference position Pt to the heel reference position Ph. The head thickness of the continuous recess part Rx is smaller than the head thickness of the first thick portion T 1 . 
     The sectional view of the head  100  at the toe reference position Pt is the same as  FIG. 6 . The sectional view of the head  100  at the heel reference position Ph is the same as  FIG. 8 . As shown in these sectional views, the weight of the head  100  is allocated to the upper portion and the lower portion. Furthermore, the center recess part Rc is provided in the head  100 . Therefore, also in the middle portion of the head, the weight of the head is allocated to the upper portion and the lower portion. 
       FIG. 12  is a back view of a head  200  according to a third embodiment. The head  200  is the same as the head  6  except for the shape of the back surface. 
     The head  200  includes a face surface (not shown in the drawing), aback surface  216 , a sole surface  218 , and a top blade  220 . The head  200  further includes a hosel  222 . 
     The top blade  220  constitutes an upper surface of the head  200 . The top blade  220  is located on the upper side of the face surface. The top blade  220  is located on the upper side of the back surface  216 . The top blade  220  extends between an upper edge of the face surface and an upper edge of the back surface  216 . 
     The back surface  216  includes a top-side region B 1  and a sole-side region B 2 . The top-side region B 1  is located on the upper side of the sole-side region B 2 . The top-side region B 1  is located between the sole-side region B 2  and the top blade  220 . The sole-side region B 2  is located on the lower side of the top-side region B 1 . The sole-side region B 2  is located between the top-side region B 1  and the sole surface  218 . 
     The top-side region B 1  includes a toe recess part Rt and a heel recess part Rh. The top-side region B 1  further includes a center recess part Rc. The center recess part Rc is formed between the toe recess part Rt and the heel recess part Rh. Although the second thick portion T 2  is provided in the above-described head  6 , the head  200  does not include the second thick portion T 2 . 
     The center recess part Rc is located in a region that includes the sweet spot SS. The center recess part Rc is located in a region that includes the face center Fc. 
     The toe recess part Rt is continuous with the center recess part Rc. The center recess part Rc is continuous with the heel recess part Rh. The toe recess part Rt, the heel recess part Rh and the center recess part Rc are continuous with each other, thereby forming a continuous recess part Rx that extends from the toe side to the heel side. The continuous recess part Rx continuously extends at least from the toe reference position Pt to the heel reference position Ph. The head thickness of the continuous recess part Rx is smaller than the head thickness of the first thick portion T 1 . 
     The sectional view of the head  200  at the toe reference position Pt is the same as  FIG. 6 . The sectional view of the head  200  at the heel reference position Ph is the same as  FIG. 8 . As shown in these sectional views, the weight of the head  200  is allocated to the upper portion and the lower portion. In addition, the center recess part Rc is provided in the head  200 . Therefore, also in the middle portion of the head, the weight of the head is allocated to the upper portion and the lower portion. 
     The back surface  216  (top-side region B 1 ) includes a toe thick portion Tt. The toe thick portion Tt is provided on the toe side relative to the toe reference position Pt. The toe thick portion Tt is provided on the toe side of the toe recess part Rt. The head thickness of the toe thick portion Tt is greater than the head thickness of the toe recess part Rt. A toe-side edge of the toe thick portion Tt forms a part of the edge of the head  200 . Because of the presence of the toe thick portion Tt, the toe recess part Rt does not reach the toe-side edge of the head  200  (back surface  216 ). As a result, the head  200  does not include the above-described side recess part S 1 . 
     The back surface  216  (top-side region B 1 ) includes a heel thick portion Th. The heel thick portion Th is provided on the heel side relative to the heel reference position Ph. The heel thick portion Th is provided on the heel side of the heel recess part Rh. The head thickness of the heel thick portion Th is greater than the head thickness of the heel recess part Rh. A heel-side edge of the heel thick portion Th forms a part of an edge of the back surface  216 . Because of the presence of the heel thick portion Th, the heel recess part Rh does not reach the heel-side edge of the back surface  216 . 
     Thus, the head  200  includes the toe thick portion Tt and the heel thick portion Th. The head  200  is a head in which the toe thick portion Tt and the heel thick portion Th are added to the head  100 . 
     These embodiments exhibit the following advantageous effects. 
     In the head  6 , the head  100 , and the head  200 , the toe recess part Rt and the heel recess part Rh are formed. Saved weight produced by providing these recess parts is distributed to the first thick portion T 1  or the sole-side region B 2 . This distribution of the weight increases a up-down MI. Although the head can be rotated due to variations of hitting points in the up-down direction, the increased up-down MI suppresses the rotation. As a result, variations in flight distance are suppressed. The saved weight means a weight removed by forming the recess parts. 
     Note that the up-down MI means a moment of inertia about a rotation axis that passes through the center of gravity of the head and is parallel to the toe-heel direction. A left-right MI to be described later means a moment of inertia about a rotation axis that passes through the center of gravity of the head and is parallel to the up-down direction. 
     As described above, variations in hitting points in the up-down direction rotate the head. When a ball collides with the face at a hitting point away from the sweet spot SS, the head is rotated in reaction of the collision. The rotation of the head is conveyed to hands as feeling. The rotation of the head worsens hit feeling. The increased up-down MI suppresses the rotation of the head, whereby the hit feeling is improved. 
     In a general cavity back iron, a large saved weight caused by the cavity is distributed to the whole circumference of the head, and thus a MI about a shaft axis and a center-of-gravity distance are large. The MI about the shaft axis means a moment of inertia of the head about a rotation axis that is the shaft axis line (center line of the hosel hole). The center-of-gravity distance means a distance between the shaft axis line and the center of gravity of the head. 
     In such a cavity back iron, the up-down MI and the left-right MI are increased, and thus a sweet area is enlarged. On the other hand, when the MI about the shaft axis and the center-of-gravity distance are large, controllability deteriorates. The controllability means the easiness of operation for closing or opening the face surface. Professional golf players and advanced-level golf players particularly place importance on whether or not they can control the face surface as intended. That is, professional golf players and advanced-level golf players emphasize the controllability. 
     In the head  6  and the head  100 , the weight is redistributed to the upper portion and the lower portion of the head. This redistribution hardly affects the MI about the shaft axis and the center-of-gravity distance. The MI about the shaft axis and the center-of-gravity distance in these heads are similar to those of a general flat back iron. Therefore, a high controllability is maintained. Also in the head  200 , the weight distributed to the toe thick portion Tt and the heel thick portion Th is smaller than that of a general cavity back iron. Therefore, the controllability is maintained also in the head  200 . Thus, in the respective heads of the above-described embodiments, variations in flight distance cased by variations in hitting points in the up-down direction are suppressed, the hit feeling is improved, and the high controllability is maintained. 
     In the head  6 , the second thick portion T 2  is provided. The second thick portion T 2  is located in the region including the sweet spot SS. Hitting points are concentrated in the vicinity of the sweet spot SS. The head thickness of the vicinity of hitting points is increased by the second thick portion T 2 . The second thick portion T 2  suppresses deformation and vibration caused by hitting. The second thick portion T 2  improves hit feeling. 
     In the head  6 , the second thick portion T 2  includes the width changing portion T 21 . That is, in at least a part of the second thick portion T 2 , the width of the second thick portion T 2  increases toward the sole surface. It has been found that variations in hitting points become large on the sole side relative to the sweet spot SS, through an analysis of hitting points&#39; distribution based on data of actual ball hits by many golf players. Because of the presence of the width changing portion T 21 , the shape of the second thick portion T 2  corresponds to the hitting points&#39; distribution. For this reason, the hit feeling is improved. 
     A double-pointed arrow WT 2  in  FIG. 3B  shows the minimum value of the toe-heel direction width of the second thick portion T 2 . In light of hit feeling, WT 2  is preferably greater than or equal to 5 mm, more preferably greater than or equal to 10 mm, and still more preferably greater than or equal to 15 mm. In light of increase in the up-down MI, WT 2  is preferably less than or equal to 30 mm, more preferably less than or equal to 25 mm, and still more preferably less than or equal to 20 mm. 
     In the head  6 , the head  100  and the head  200 , the angle θ1 is smaller than the angle θ2. That is, the lower edge of the first thick portion T 1  extends in a direction nearer to a ground surface than the extending direction of the top blade. For this reason, the width of the first thick portion T 1  is increased on the toe side, whereby the weight distributed to the first thick portion T 1  is increased. As a result, the effect of increasing the up-down MI is further enhanced. 
     When the lower edge of the first thick portion T 1  is inclined upward as going to the toe side, θ1 is defined as a positive value. In the embodiment shown in  FIG. 3A  and  FIG. 3B , the θ1 is the positive value. On the other hand, the lower edge of the first thick portion T 1  is inclined downward as going to the toe side, the θ1 is defined as a negative value. θ1 may be a negative value. However, when θ1 is a negative value, the toe recess part Rt is narrowed, and the up-down MI can be reduced. In this respect, θ1 is preferably not a negative value. In light of increase in the up-down MI, θ 1  is preferably greater than or equal to 0 degree, and more preferably greater than 0 degree. When θ1 is excessively large, the area of the first thick portion T 1  is decreased, and the up-down MI can be reduced. In this respect, θ1 is preferably less than or equal to 20 degrees, more preferably less than or equal to 16 degrees, and still more preferably less than or equal to 12 degrees. 
     In light of increase in the up-down MI, a difference [θ2−θ1] between the angle θ2 and the angle θ1 is preferably large. In this respect, [θ2−θ1] is preferably greater than or equal to 7 degrees, more preferably greater than or equal to 8 degrees, and still more preferably greater than or equal to 9 degrees. In light of retaining an area for providing the toe recess part Rt, [θ2−θ1] is preferably less than or equal to 16 degrees, more preferably less than or equal to 15 degrees, and still more preferably less than or equal to 14 degrees. 
     The above-described preferable values for [θ2−θ1] are applicable to [θ2 min−θ1max]. 
     In the head  6 , the head  100  and the head  200 , the angle θ1 is smaller than the angle θ2. That is, the lower edge of the first thick portion T 1  extends in a direction nearer to the ground surface than the extending direction of the top blade. For this reason, the width of the first thick portion T 1  is increased on the toe side, whereby the head rigidity on the toe side is enhanced. As a result, although the toe recess part Rt is present, an excessively large deformation of the head in hitting on the toe side is suppressed, and deterioration of hit feeling is suppressed. 
     Because of the presence of the toe recess part Rt, the side recess part S 1  is formed on the toe side surface ST in the head  6  and the head  100 . The side recess part S 1 , however, is disposed on a location that is invisible from the reference viewpoint. Therefore, the contour of the toe side of the head in addressing does not look strange, and the strange feeling does not arise. 
     In the head  6  and the head  100 , the toe recess part Rt includes the toe upper inclined surface Rt 11 , and the toe upper inclined surface Rt 11  forms the side recess part S 1 . For example, when the toe recess part Rt is disposed on a further upper side, the side recess part S 1  can located at a position that is visible in addressing. Even when the side recess part S 1  is visible in addressing, the side recess part S 1  looks similar to the toe-side end of a normal head because of the presence of the toe upper inclined surface Rt 1 . For this reason, the strange feeling in addressing is suppressed. 
     A double-pointed arrow W 11  in  FIG. 5  shows a width of the toe upper inclined surface Rt 11  in the side recess part S 1 . The width W 11  is measured along the up-down direction. In light of suppressing the strange feeling in addressing when the side recess part S 1  is visible, the width W 11  is preferably greater than or equal to 4 mm, more preferably greater than or equal to 6 mm, and still more preferably greater than or equal to 8 mm. The saved weight produced by forming the toe recess part Rt is preferably large in order to increase the up-down MI. In this respect, the width W 11  is preferably less than or equal to 14 mm, more preferably less than or equal to 12 mm, and still more preferably less than or equal to 10 mm. 
     In the head  6 , the head  100  and the head  200 , the toe recess part Rt includes the toe upper inclined surface Rt 11 . The toe upper inclined surface Rt 11  suppresses a sharp decrease in the head thickness. Although the toe recess part Rt is likely to be deformed due to a small head thickness thereof, the toe upper inclined surface Rt 11  prevents the toe recess part Rt from being excessively deformed. For this reason, even when a hitting point is located in the region of the toe recess part Rt, the hit feeling is good. 
     In the head  6 , the toe recess part Rt includes the toe lateral inclined surface Rt 3 . The toe lateral inclined surface Rt 3  suppresses a shape decrease in the head thickness. Although the toe recess part Rt is likely to be deformed due to its small head thickness, the toe lateral inclined surface Rt 3  prevents the toe recess part Rt from being excessively deformed. For this reason, even when a hitting point is deviated to fall on the toe side of the second thick portion T 2 , the hit feeling is good. 
     In the head  6 , the head  100 , and the head  200 , the heel recess part Rh includes the heel upper inclined surface Rh 11 . The heel upper inclined surface Rh 11  suppresses a shape decrease in the head thickness. Although the heel recess part Rh is likely to be deformed due to a small head thickness thereof, the heel upper inclined surface Rh 11  prevents the heel recess part Rh from being excessively deformed. For this reason, even when a hitting point is located in a region on the heel thick portion Th, the hit feeling is good. 
     In the head  6 , the heel recess part Rh includes the heel lateral inclined surface Rh 3 . The heel lateral inclined surface Rh 3  suppresses a shape decrease in the head thickness. Although the heel recess part Rh is likely to be deformed due to its small head thickness, the heel lateral inclined surface Rh 3  prevents the heel recess part Rh from being excessively deformed. For this reason, when a hitting point is deviated to fall on the heel side of the second thick portion T 2 , the hit feeling is good. 
     In the head  100  ( FIG. 11 ), the center recess part Rc is provided instead of the second thick portion T 2 . For this reason, the up-down MI is further increased. As a result, variations in flight distances caused by variations in hitting points in the up-down direction are suppressed, and furthermore, hit feeling is improved. In the head  200  ( FIG. 12 ), since the toe thick portion Tt and the heel thick portion Th are provided, the left-right MI is also increased in addition to the increased up-down MI. For this reason, not only deviation of the head in the vertical direction but also deviation of the head in the horizontal direction is suppressed. 
     In light of increasing a weight distributed to the upper portion of the head and enhancing the up-down MI, the head thickness of the first thick portion T 1  is preferably greater than or equal to 4.5 mm, more preferably greater than or equal to 4.7 mm, and still more preferably greater than or equal to 4.9 mm. In light of preventing the center of gravity of the head from being an excessively high position, the head thickness of the first thick portion T 1  is preferably less than or equal to 6.5 mm, more preferably less than or equal to 6.3 mm, and still more preferably less than or equal to 6.1 mm. 
     In light of hit feeling, the head thickness of the second thick portion T 2  is preferably greater than or equal to 4.5 mm, more preferably greater than or equal to 4.7 mm, and still more preferably greater than or equal to 4.9 mm. In view of restriction on head weight, the head thickness of the second thick portion T 2  is preferably less than or equal to 6.5 mm, more preferably less than or equal to 6.3 mm, and still more preferably less than or equal to 6.1 mm. 
     In light of enhancing the up-down MI, the minimum value of the head thickness in the toe recess part Rt is preferably less than or equal to 3.6 mm, more preferably less than or equal to 3.4 mm, and still more preferably less than or equal to 3.2 mm. In view of the strength of the head, the minimum value of the head thickness in the toe recess part Rt is preferably greater than or equal to 1.8 mm, more preferably greater than or equal to 2.0 mm, and still more preferably greater than or equal to 2.2 mm. 
     In light of enhancing the up-down MI, the minimum value of the head thickness in the heel recess part Rh is preferably less than or equal to 3.6 mm, more preferably less than or equal to 3.4 mm, and still more preferably less than or equal to 3.2 mm. In view of the strength of the head, the minimum value of the head thickness in the heel recess part Rh is preferably greater than or equal to 1.8 mm, more preferably greater than or equal to 2.0 mm, and still more preferably greater than or equal to 2.2 mm. 
     The head thickness of the first thick portion T 1  is denoted by Tc1 (mm), the head thickness of the second thick portion T 2  is denoted by Tc2 (mm), the minimum value of the head thickness in the toe recess part Rt is denoted by Tc3 (mm), and the minimum value of the head thickness in the heel recess part Rh is denoted by Tc4 (mm) (see  FIG. 6  to  FIG. 8 ). Hereinafter, a difference [Tc1−Tc3], a difference [Tc1−Tc4], a difference [Tc2−Tc3], and a difference [Tc2−Tc4] are considered. 
     In light of increase in the up-down MI, [Tc1−Tc3] is preferably greater than or equal to 2.0 mm, more preferably greater than or equal to 2.1 mm, and still more preferably greater than or equal to 2.2 mm. In view of preferable head thickness in each portion, [Tc1−Tc3] is preferably less than or equal to 3.5 mm, more preferably less than or equal to 3.3 mm, and still more preferably less than or equal to 3.1 mm. 
     In light of increase in the up-down MI, [Tc1−Tc4] is preferably greater than or equal to 2.0 mm, more preferably greater than or equal to 2.1 mm, and still more preferably greater than or equal to 2.2 mm. In view of preferable head thickness in each portion, [Tc1−Tc4] is preferably less than or equal to 3.5 mm, more preferably less than or equal to 3.3 mm, and still more preferably less than or equal to 3.1 mm. 
     In light of increase in the up-down MI and hit feeling, [Tc2-Tc3] is preferably greater than or equal to 2.0 mm, more preferably greater than or equal to 2.1 mm, and still more preferably greater than or equal to 2.2 mm. In view of preferable head thickness in each portion, [Tc2-Tc3] is preferably less than or equal to 3.5 mm, more preferably less than or equal to 3.3 mm, and still more preferably less than or equal to 3.1 mm. 
     In light of increase in the up-down MI and hit feeling, [Tc2-Tc4] is preferably greater than or equal to 2.0 mm, more preferably greater than or equal to 2.1 mm, and still more preferably greater than or equal to 2.2 mm. In view of preferable head thickness in each portion, [Tc2-Tc4] is preferably less than or equal to 3.5 mm, more preferably less than or equal to 3.3 mm, and still more preferably less than or equal to 3.1 mm. 
     The present disclosure can be applied to all iron type golf club heads. An iron type hybrid (iron type utility) golf club head having a plane face surface is included in the iron type golf club heads in the present application. 
     The above descriptions are merely illustrative examples, and various modifications can be made.