Abstract:
A chin guard support mechanism includes first and second fixed-side members, and a moving-side member fixed to the chin guard. When the chin guard pivots forward from a down position in a rising direction, an annular following surface provided on the moving-side member pivots forward while following an annular followed surface provided on the second fixed-side member to make the chin guard rise while moving forward. It is possible to provide a helmet that allows the chin guard support mechanism capable of relatively excellently raising/lowering the chin guard to have a simple structure, allows to operate the chin guard support mechanism smoothly, obviates the necessity of making the structure in a region including an end of the chin guard including the chin guard support mechanism and a vicinity thereof bulky, and obviates the necessity of making the widthwise size of the helmet large.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a helmet including left and right chin guard support mechanisms provided on a main cap body, and a chin guard whose regions including left and right ends and vicinities thereof are pivotally attached to the left and right chin guard support mechanisms, respectively. 
       BACKGROUND OF THE INVENTION 
       [0002]    A helmet configured as described above is conventionally known, as disclosed in US 2009/0100576 A1. In the helmet (to be referred to as “the conventional helmet” hereinafter) disclosed in US 2009/0100576 A1, each of the left and right chin guard support mechanisms includes a fixed-side unit fixed to the left side surface or right side surface of the main cap body, and a pivotal-side unit fixed to a region including the left or right end of the chin guard and a vicinity thereof. The fixed-side unit is provided with a first longitudinal guide hole that extends forward obliquely above, and a second longitudinal guide hole that is arranged under the first longitudinal guide hole and extends forward obliquely below. The longitudinal direction of the first longitudinal guide hole is substantially perpendicular to that of the second longitudinal guide hole. The first and second longitudinal guide holes extend substantially linearly. The pivotal-side unit is provided with a first connection portion that is inserted into the first longitudinal guide hole and guided by the first longitudinal guide hole, and a second connection portion that is inserted into the second longitudinal guide hole and guided by the second longitudinal guide hole. 
         [0003]    In the conventional helmet configured as described above, when the chin guard moves from the lowermost position to the uppermost position, the second connection portion moves from the upper end side of the second longitudinal guide hole to its lower end side. At the same time, the first connection portion moves from the lower end side of the first longitudinal guide hole to its upper end side and then from the upper end side to the lower end side. Hence, during the movement from the lowermost position to the midpoint of rise, the chin guard slightly moves forward, too. In addition, during the rise from the midpoint of rise to the uppermost position, the chin guard slightly moves backward, too. When lowering from the uppermost position to the lowermost position contrary to the rise, the chin guard slightly moves forward and then slightly moves backward, as in the rise. 
         [0004]    However, in the left or right chin guard support mechanism of the conventional helmet, the fixed-side unit having the first and second longitudinal guide holes, and the pivotal-side unit including the first and second connection portions need to be provided between the left side surface or the right side surface of the main cap body and a region including the left or right ends of the chin guard and a vicinity thereof. For this reason, the structure of each chin guard support mechanism is relatively complex, and it may be difficult to smoothly operate the chin guard support mechanisms. In addition, a space to provide the fixed-side unit and the pivotal-side unit is necessary on the left or right side surface of the main cap body and the region including the left or right ends of the chin guard and the vicinity thereof. For this reason, the structure in a region including the end of the chin guard including the left or right chin guard support mechanism and a vicinity thereof may be bulky, and the widthwise size of the helmet including the left and right chin guard support mechanisms may be large. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is aimed at properly solving the above-described problems of the conventional helmet using a relatively simple arrangement. 
         [0006]    The present invention therefore has an object to provide a helmet that allows a chin guard support mechanism capable of relatively excellently raising/lowering a chin guard to have a relatively simple structure, allows to operate the chin guard support mechanism relatively smoothly, obviates the necessity of making the structure in a region including an end of the chin guard including the chin guard support mechanism and a vicinity thereof particularly bulky, and obviates the necessity of making the widthwise size of the helmet including the left chin guard support mechanism and the right chin guard support mechanism particularly large. 
         [0007]    It is another object of the present invention to provide a helmet that allows a chin guard support mechanism capable of relatively excellently raising/lowering both a chin guard and a shield plate to have a relatively simple structure, allows to operate the chin guard support mechanism relatively smoothly, obviates the necessity of making the structure in a region including an end of the chin guard including the chin guard support mechanism and a vicinity thereof particularly bulky, and obviates the necessity of making the widthwise size of the helmet including the left chin guard support mechanism and the right chin guard support mechanism particularly large. 
         [0008]    It is still another object of the present invention to provide a helmet capable of preventing the rise of a shield plate more than necessary because the shield plate rises by a first predetermined angle smaller than a second predetermined angle when the shield plate is raised while keeping a chin guard held at the lowermost position, and also capable of preventing the rise of the chin guard and the shield plate more than necessary because when the chin guard is raised by an angle larger than the first predetermined angle, the shield plate can also rise by the larger angle together with the chin guard and does not impede the rise of the chin guard when the chin guard rises by the angle larger than the first predetermined angle, and both the chin guard and the shield plate rise by only the second predetermined angle. 
         [0009]    It is yet another object of the present invention to provide a helmet capable of relatively properly preventing, using a relatively simple arrangement, an unnecessary linear forward and backward movement of a first moving-side member with respect to a second fixed-side member at the time of forward and backward pivot of the former with respect to the latter. 
         [0010]    It is still another object of the present invention to provide a helmet capable of more relatively properly preventing, using a simpler arrangement, an unnecessary linear forward and backward movement of a first moving-side member with respect to a second fixed-side member at the time of forward and backward pivot of the former with respect to the latter. 
         [0011]    The present invention is directed to a helmet including left and right chin guard support mechanisms provided on a main cap body, and a chin guard whose regions including left and right ends and vicinities thereof are pivotally attached to the left and right chin guard support mechanisms, respectively, each of the left and right chin guard support mechanisms including a first fixed-side member fixed to the main cap body, and a first moving-side member fixed to the chin guard, wherein each of the left and right chin guard support mechanisms further includes a second fixed-side member fixed to the first fixed-side member, a convex or concave annular followed surface is provided on the second fixed-side member, a concave or convex annular following surface capable of pivoting forward and backward while following the convex or concave annular followed surface is provided on the first moving-side member, and when the chin guard pivots forward from a down position in a rising direction, the annular following surface pivots forward while following the annular followed surface to make the chin guard rise while moving forward. 
         [0012]    Note that according to the first aspect of the present invention, the helmet further comprises a shield plate whose regions including left and right ends and vicinities thereof are pivotally attached to the left and right chin guard support mechanisms, respectively, wherein each of the left and right chin guard support mechanisms further includes a second moving-side member supported to be movable forward and backward substantially in forward and backward directions with respect to the first moving-side member, a second followed surface is provided on the first moving-side member, a second following surface capable of moving forward and backward while following the second followed surface is provided on the shield plate, and when the shield plate pivots forward from the down position in the rising direction with respect to the chin guard, the second following surface moves forward while following the second followed surface to make the shield plate rise while moving forward. According to a mode of the first aspect of the present invention, the helmet further comprises a first stopper portion provided on the second moving-side member, and a first stopped portion provided on the shield plate to be able to abut against the first stopper portion, a second stopper portion provided on the first fixed-side member, and a second stopped portion provided on the first moving-side member, and a third stopper portion provided on the second fixed-side member, and a third stopped portion provided on the shield plate, wherein when the shield plate rises by a first predetermined angle with respect to the chin guard, the first stopped portion abuts against the first stopper portion to prevent further rise of the shield plate, when the chin guard rises by a second predetermined angle larger than the first predetermined angle with respect to the main cap body, the second stopped portion abuts against the second stopper portion to prevent further rise of the chin guard, and when the shield plate substantially rises by the second predetermined angle with respect to the main cap body, the third stopped portion abuts against the third stopper portion to prevent further rise of the shield plate. In this case, the first predetermined angle preferably ranges from 30° to 60°, and more preferably ranges from 40° to 56°. The second predetermined angle preferably ranges from 60° to 100°, and more preferably ranges from 70° to 90°. 
         [0013]    According to the second aspect of the present invention, the convex or concave annular followed surface includes a convex annular followed surface, and the concave or convex annular following surface includes a concave annular following surface. 
         [0014]    According to the third aspect of the present invention, the concave or convex annular following surface substantially always contacts the convex or concave annular followed surface at three portions spaced apart from each other independently of a forward and backward pivot position of the first moving-side member with respect to the second fixed-side member, and the contacts at the three portions prevent an unnecessary linear forward and backward movement of the first moving-side member with respect to the second fixed-side member. According to a mode of the third aspect, the convex or concave annular followed surface includes a convex annular followed surface, the concave or convex annular following surface includes a concave annular following surface, and the contacts at the three portions include: 
         [0015]    (i) a contact between a peripheral surface of a first convex followed surface portion of the convex annular followed surface and, out of the concave annular following surface, a region including a peripheral surface of a first concave following surface portion having a substantially same shape as the first convex followed surface portion and a vicinity thereof, 
         [0016]    (ii) a contact between a peripheral surface of a second convex followed surface portion of the convex annular followed surface and, out of the concave annular following surface, a region including a peripheral surface of a second concave following surface portion longer than the second convex followed surface portion in a circumferential direction and a vicinity thereof, and 
         [0017]    (iii) a contact between a peripheral surface of a followed surface main body portion having a substantially circular shape between the first convex followed surface portion and the second convex followed surface portion out of the convex annular followed surface, and a peripheral surface of a following surface portion having a bent shape of the concave annular following surface. 
         [0018]    The above, and other, objects, features and advantages of present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a perspective view of a helmet according to an embodiment of the present invention with a chin guard in a lowermost state; 
           [0020]      FIG. 2  is a perspective view of the helmet shown in  FIG. 1  with the chin guard in an uppermost state; 
           [0021]      FIG. 3  is a left side view of the helmet shown in  FIG. 1 ; 
           [0022]      FIG. 4  is a left side view of the helmet shown in  FIG. 3 ; 
           [0023]      FIG. 5  is a left side view showing a state in which a support plate is attached to the left side surface of the main cap body outer shell of the helmet shown in  FIG. 4  in the initial stage of an assembly process; 
           [0024]      FIG. 6  is a left side view showing a state in which a chin guard attached to the main cap body outer shell shown in  FIG. 5 , and a shield base attached to the chin guard are spaced apart from each other; 
           [0025]      FIG. 7  is a left side view showing a state in which the chin guard shown in  FIG. 6  with the shield base attached, and a shield pivot member attached to the shield base are spaced apart from each other; 
           [0026]      FIG. 8  is a left side view showing a state in which the chin guard shown in  FIG. 7  with the shield pivot member attached to the shield base, and a shaft member with washer that pivotally supports the shield base are spaced apart from each other; 
           [0027]      FIG. 9  is a left side view showing a state in which the chin guard shown in  FIG. 8  is incorporated in the main cap body outer shell by bolting the shaft member with washer to a support plate; 
           [0028]      FIG. 10  is a left side view of a shield plate shown in  FIG. 3 ; 
           [0029]      FIG. 11  is a partial left side view of the helmet shown in  FIG. 3 ; 
           [0030]      FIG. 12  is a left side view of the helmet shown in  FIG. 11  with the shield plate being in the uppermost state; 
           [0031]      FIG. 13  is a partial left side view showing the lowermost state of the chin guard of the helmet shown in  FIG. 3  and a state in which the chin guard has pivoted by 1° from the lowermost state in the rising direction; 
           [0032]      FIG. 13A  is a partially enlarged left side view of the lowermost state of the chin guard shown in  FIG. 13 ; 
           [0033]      FIG. 13B  is a partially enlarged left side view of the state shown in  FIG. 13  in which the chin guard has pivoted by 1° from the lowermost state in the rising direction; 
           [0034]      FIG. 14  is a left side view showing the state shown in  FIG. 13  in which the chin guard of the helmet in  FIG. 13  has raised by 1°, and a state in which the chin guard has further pivoted from the state shown in  FIG. 13  in the rising direction to pivot by 2° from the lowermost state in the rising direction; 
           [0035]      FIG. 15  is a left side view showing the state shown in  FIG. 14  in which the chin guard of the helmet in  FIG. 14  has raised by 2°, and a state in which the chin guard has further pivoted from the state shown in  FIG. 14  in the rising direction to pivot by 4° from the lowermost state in the rising direction; 
           [0036]      FIG. 16  is a left side view showing the state shown in  FIG. 15  in which the chin guard of the helmet in  FIG. 15  has raised by 4°, and a state in which the chin guard has further pivoted from the state shown in  FIG. 15  in the rising direction to pivot by 8° from the lowermost state in the rising direction; 
           [0037]      FIG. 17  is a partial left side view showing a state shown in which the chin guard of the helmet shown in  FIG. 3  has pivoted by 16° from the lowermost state in the rising direction; 
           [0038]      FIG. 18  is a partial left side view showing a state shown in which the chin guard of the helmet shown in  FIG. 3  has pivoted by 80° from the lowermost state to the uppermost state in the rising direction; and 
           [0039]      FIG. 19  is a partial left side view showing the helmet whose chin guard has pivoted by 1° from the lowermost state in the rising direction and illustrating one reference example in which the pivot support of the chin guard of the helmet shown in  FIG. 13  is assumed to be set at a fixed position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    An embodiment in which the present invention is applied to a full-face-type helmet including a chin guard capable of rising/lowering will now be described with reference to the accompanying drawings in “1. Schematic Arrangement of Helmet as a Whole”, “2. Arrangement of Chin Guard Support Mechanism” and “3. Operation of Chin Guard Support Mechanism”. 
         [0041]    1. Schematic Arrangement of Helmet as a Whole 
         [0042]    As shown in  FIGS. 1 to 4 , a full-face-type helmet  1  with a chin guard  6  capable of rising/lowering includes a full-face-type cap body  2  to be put on the head of a wearer such as a motorbike rider and including the chin guard  6  capable of rising/lowering, a shield plate  4  capable of opening/closing a window opening  3  formed in front of the cap body  2  to face a portion between the forehead and the chin of the wearer (that is, a substantially center of the face), and a pair of left and right chin bands (not shown) attached to the inside of the cap body  2 . 
         [0043]    The cap body  2  shown in  FIGS. 1 to 4  includes a main cap body  5  that can have a substantially same shape as that of the cap body of a jet-type helmet, and the chin guard  6  serving as an auxiliary cap body attached to the main cap body  5  via a pair of left and right pivotal support means  7  on the left and right sides of the main cap body  5  to pivot forward and backward, as is known. Hence, a large window portion  8  is formed in the main cap body  5  by largely cutting the front surface from the lower end. The chin guard  6  includes a chin cover  6   a  that bends to bulge forward, and a pair of left and right attachment portions  6   b  that extend upward from the left and right ends of the chin cover  6   a  and are pivotally supported on the left and right sides of the cap body  2  by the pair of left and right pivotal support means  7  (in other words, chin guard support mechanisms  23  to be described later) to pivot forward and backward, as is known. When the chin guard  6  has pivoted downward with respect to the main cap body  5  to be located at the down position (especially the lowermost position shown in  FIGS. 1 and 3 ), the chin guard  6  functions as a chin cover means for covering the chin of the wearer and closes the lower portion of the window portion  8 . The window opening  3  is thus formed by the upper portion of the window portion  8 . Hence, the window opening  3  is formed from a region surrounded by the upper edge of the window portion  8  of the main cap body  5  and an upper edge  11  of the chin guard  6 . 
         [0044]    The shield plate  4  shown in  FIGS. 1 to 4  can be made of a hard transparent or semitransparent material such as polycarbonate or another hard synthetic resin, as is known. The shield plate  4  is attached to the main cap body  5  via a pair of left and right pivotal support means  12  (in other words, shield pivot members  25  to be described later) on the left and right sides of the main cap body  5 . Note that when the chin guard  6  is located at the down position (especially the lowermost position shown in  FIGS. 1 and 3 ) and functions as a chin cover means, the shield plate  4  closes the window opening  3  at its backward position (that is, down position) and opens the window opening  3  at its forward position (that is, up position). 
         [0045]    The main cap body  5  shown in  FIGS. 1 to 4  can include a jet-type outer shell  13  that constitutes the outer wall of the main cap body  5 , a rim member  14  having a substantially U-shaped section and attached to substantially all around the end of the outer shell  13  by adhesion or the like, and a main cap body backing member (not shown) attached in abutment with the inner surface of the outer shell  13  by adhesion or the like, as is known. Note that the outer shell  13  can be made of a composite material formed by lining the inner surface of a strong shell main body made of FRP or another hard synthetic resin with a flexible sheet such as nonwoven fabric, as is known. The rim member  14  having the substantially U-shaped section can be made of a highly flexible elastic material such as foamed vinyl chloride, synthetic rubber, or another soft synthetic resin, as is known. 
         [0046]    The main cap body backing member can include a main cap body shock absorbing liner attached to the inner surface of the main cap body outer shell  13  shown in  FIGS. 1 to 4  by adhesion or the like, and a main cap body block-shaped interior pad and a main cap body backing cover which are sequentially attached to substantially cover the inner surface of the shock absorbing liner, as is known. The main cap body shock absorbing liner can be made of a material having appropriate rigidity and appropriate plasticity such as foamed polystyrene or another synthetic resin, as is known. The main cap body block-shaped interior pad can be formed from one or a plurality of highly flexible elastic materials such as urethane foam or another synthetic resin, and bag-shaped porous nonwoven fabric that covers the inner and outer surfaces of the elastic material, as is known. The main cap body backing cover can be made of porous nonwoven fabric whose surface facing the main cap body shock absorbing liner is laminated with a layer of a highly flexible elastic material such as urethane foam or another synthetic resin, as is known. 
         [0047]    The chin guard  6  shown in  FIGS. 1 to 4  can include an outer shell  15  that constitutes the outer wall of the chin guard  6 , a rim member (not shown) having a substantially E-shaped section and attached to a portion of the end of the outer shell  15  (more specifically, the upper end of the outer shell  15 ) by adhesion or the like, and a chin guard backing member (not shown) attached in abutment with the inner surface of the outer shell  15  by adhesion or the like, as is known. Note that the outer shell  15  and the rim member having the substantially E-shaped section can be made of the same materials as already described concerning the outer shell  13  and the rim member  14  having the substantially U-shaped section for the main cap body, as is known. 
         [0048]    The chin guard backing member can include a chin guard shock absorbing liner attached to the inner surface of the chin guard outer shell  15  shown in  FIGS. 1 to 4  by adhesion or the like, and a chin guard backing cover attached to substantially cover the inner surface of the shock absorbing liner, as is known. The chin guard shock absorbing liner can be made of a material having appropriate rigidity and appropriate plasticity such as urethane foam rubber or another synthetic resin. The chin guard backing cover can be made of artificial leather formed from a synthetic resin such as polyvinyl chloride, or another fabric. In addition, an air vent forming member  16  for the top of head is attached to the outer surface of the main cap body  5  in a region including the top of head and a vicinity thereof, as shown in  FIGS. 1 to 4 . An air vent  17  is formed in the chin cover  6   a  of the chin guard  6 . Note that the chin guard  6  is provided with an unlock operation button  18  to be pressed to unlock a lock means (not shown) such as a lock pawl for locking the chin guard  6  at the lowermost position, as shown in  FIG. 2 . In addition, the main cap body  5  includes, on its outer surface, a lock pin  19  that engages with the lock means (not shown) to hold the chin guard  6  at the lowermost position, as shown in  FIGS. 2 ,  4  and  5 . 
         [0049]    The main cap body  5  is provided with a pair of left and right support plates  21  to be used to support the shield plate  4  and the chin guard  6  on the main cap body  5 , as shown in  FIGS. 3 to 5 . Each of the pair of left and right support plates  21  can be a substantially plate-shaped member made of an appropriate material, for example, a synthetic resin such as polyacetal resin or ABS resin, as shown in  FIG. 5 . The support plates  21  may be fixed to the main cap body outer shell  13  by attachment screws  22 . Note that the arrangement and operation of the pair of left and right chin guard support mechanisms  23  for pivotally supporting the shield plate  4  and the chin guard  6  on the main cap body  5  will be described in detail in “2. Arrangement of Chin Guard Support Mechanism” and “3. Operation of Chin Guard Support Mechanism”. 
         [0050]    2. Arrangement of Chin Guard Support Mechanism 
         [0051]    The chin guard support mechanism  23  on the left side and the chin guard support mechanism  23  on the right side of the pair of left and right chin guard support mechanisms  23  are formed to be bilaterally symmetrical to each other. Hence, the chin guard support mechanism  23  on the left side (in other words, the left side viewed from the wearer) will be described below with reference to the accompanying drawings, and a description of the chin guard support mechanism  23  on the right side will appropriately be omitted as needed. 
         [0052]    The chin guard support mechanism  23  on the left side includes constituent members described in (a) to (d): 
         [0053]    (a) the support plate  21  serving as a support portion, a base plate portion, or a first fixed-side member, and attached and fixed to the main cap body  5  by the attachment screws  22  serving as an attachment means, as shown in  FIG. 5 ; 
         [0054]    (b) a shield base  24  serving as a shield plate support portion, a shield plate base portion, or a first moving-side member, and attached and fixed to the attachment portion  6   b  of the chin guard  6 , as shown in  FIGS. 6 and 7 ; 
         [0055]    (c) a shield pivot member  25  serving as a shield pivot portion or a second moving-side member, and attached to the shield base  24  to be linearly movable forward and backward, as shown in  FIGS. 7 and 8 ; and 
         [0056]    (d) a shaft member  27  with washer serving as a second fixed-side member, and attached and fixed to the support plate  21  by a bolt  26  serving as a fixing means, as shown in  FIGS. 8 and 9 . 
         [0057]    When assembly the chin guard support mechanism  23  from the constituent members described in (a) to (d), the support plate  21  is attached to the main cap body  5 , as shown in  FIG. 5 . On the other hand, the shield base  24  is attached to the attachment portion  6   b  of the chin guard  6 , as shown in  FIG. 7 . Next, the shield pivot member  25  is attached to the shield base  24 , as shown in  FIG. 8 . The shaft member  27  with washer is fixed to the support plate  21  by the bolt  26 , as shown in  FIG. 9 . In addition, a region including the left end of the shield plate  4  and a vicinity thereof is attached to the shield pivot member  25 , thereby obtaining the helmet  1  shown in  FIGS. 1 to 4 . 
         [0058]    As shown in  FIG. 5 , the support plate  21  has, at a substantially center, an insertion hole  31  that receives the bolt  26  when the bolt  26  is screwed and fixed to the outer shell  13 . For example, four screw insertion holes  32   a  to  32   d  are formed in the shield base  24  along its outer periphery. Screws (not shown) inserted into the screw insertion holes  32   a  to  32   d  are screwed into screw holes (not shown) in the inner surface of the chin guard  6 , thereby attaching the shield base  24  to the inner surface of the attachment portion  6   b  of the chin guard  6 . For this purpose, the attachment portion  6   b  has a shape curved substantially upward and is formed into a substantially U shape fallen down sideways. The outer side surface of the outer periphery of the shield base  24  overlaps the attachment portion  6   b  along the inner surface of the outer periphery of the inner periphery of the outer periphery of the substantially U-shaped attachment portion  6   b.    
         [0059]    A cylindrical projection  33  having a cylindrical shape or the like and serving as a second stopped portion that projects outward (in other words, further inward) from the inner surface of the shield base  24  is disposed around the screw insertion hole  32   b  of the shield base  24 , as shown in  FIG. 6 . A cylindrical projection  34  having an elongated cylindrical shape or the like in a size larger than that of the cylindrical projection  33  and a relatively low profile is disposed on the outer surface of the support plate  21  in correspondence with the cylindrical projection  33 , as shown in  FIG. 5 . In addition, a columnar projection  35  having a substantially triangular prism shape fallen down sideways, which the cylindrical projection  33  can climb over, and a stopper projection  36  serving as a second stopper portion adjacent to the columnar projection  35  are disposed on the outer surface of the support plate  21  substantially in correspondence with the cylindrical projection  33 . 
         [0060]    A projection  41  that can have a substantially flat plate shape and has a substantially rectangular parallelepiped shape or the like is formed at a substantially center of the outer surface of the support plate  21  to surround the insertion hole  31 , as shown in  FIG. 5 . In this case, when  FIG. 5  is viewed two-dimensionally, out of the sides of the projection  41 , a pair of long sides facing each other are formed to be substantially parallel to each other. Since the projection  41  is fitted in a fitting hole  42  formed in the inner surface of the shaft member  27  with washer, as shown in  FIG. 9 , the shaft member  27  with washer can slide forward and backward (in other words, move forward and backward) in the substantially parallel direction. Hence, performing the forward and backward sliding before the bolt  26  serving as a fixing means is screwed and fixed into the outer shell  13  enables to easily adjust the position such as the lowermost position of the chin guard  6  (and the shield plate  4  by extension) in the forward and backward directions. A pair of openings  43   a  and  43   b  are formed in regions including both sides of the projection  41  in the longitudinal direction and vicinities thereof. A pair of projections  44   a  and  44   b  disposed on the inner surface of the shaft member  27  with washer are fitted in the pair of openings  43   a  and  43   b , respectively. This fitting allows to prevent the projection  41  from rattling in the fitting hole  42 . 
         [0061]    A rib-shaped projecting wall  45  formed into a substantially arc shape in a substantially vertical direction is disposed in a region including the front end of the support plate  21  and a vicinity thereof, as shown in  FIG. 5 . When the chin guard  6  is further raised for the intermediate up position, a projecting wall  46  of the shield base  24  runs on the projecting wall  45 . For this reason, the shield base  24  and the chin guard  6  are opened outward in the periphery of the projecting wall  46 . Hence, a portion of the chin guard  6 , which overlaps the rim member  14  above the window opening  3  of the main cap body  5  (see  FIG. 4 ), never comes into substantially contact (in other words, strongly rubs) with the rim member  14  above the window opening  3 . As a result, the chin guard  6  never damages the rim member  14  above the window opening  3  upon rising/lowering. 
         [0062]    An elongated protrusion  51  slidable in abutment with the inner surface of the shield base  24  when it pivots forward and backward is disposed in a region including the upper end of the outer surface of the support plate  21  and a vicinity thereof, as shown in  FIG. 5 . Note that the elongated protrusion  51  can be curved in an arc shape along the region including the upper end of the support plate  21  and the vicinity thereof. A plurality of elongated protrusions  51  (two in the illustrated embodiment) preferably run at a substantially equal interval. The support plate  21  has preferably a plurality of (four in the illustrated embodiment) relatively large through holes  52  to, for example, reduce the weight and save the materials. 
         [0063]    A pair of engaging pawls  53  and  54  are disposed on the outer surface of the shield base  24 , as shown in  FIGS. 6 and 7 . An engaging opening  55  is formed in the shield base  24 . Note that the pair of engaging pawls  53  and  54  and the engaging opening  55  are provided at positions corresponding to the three corners of a substantially equilateral triangle. On the other hand, the shield base  24  is provided with a first spring engaging convex portion  56  near the engaging pawl  53 . The shield base  24  is also provided with a second spring engaging convex portion  57  near the projecting wall  46 . Note that the shield base  24  is provided with first and second spring relief openings  61  and  62  corresponding to the first and second spring engaging convex portions  56  and  57 , respectively. In addition, an engaging opening  63  that engages with an engaging pawl  64  provided in a region including the distal end of the attachment portion  6   b  of the chin guard  6  and a vicinity thereof is provided in a region including the upper end and a vicinity thereof in a region including the front end of the shield base  24  and a vicinity thereof. 
         [0064]    An opening  66  whose edge forms a concave annular following surface  65  is formed at a substantially center of the shield base  24 , as shown in  FIGS. 6 and 7 . A projecting wall  72  whose front end surface forms a convex followed surface  71  serving as the second followed surface is provided at a substantially center in a region including the front end of the shield base  24  and a vicinity thereof. Preferably a plurality of engaging grooves  74 , in which preferably a plurality of elongated protrusions  73  formed on the inner surface of the attachment portion  6   b  of the chin guard  6  are fitted, are formed in regions including the outer portions on the upper and lower sides of the shield base  24  and vicinities thereof. 
         [0065]    The shield pivot member  25  includes a pivot member main body  75 , an unlock operation member  76  attached to the pivot member main body  75  to be linearly movable forward and backward, and a guide pin  77  disposed on the pivot member main body  75  to guide the unlock operation member  76  such that it is linearly movable forward and backward, as shown in  FIGS. 7 and 8 . The operation member  76  has a long hole  81  to receive the guide pin  77 . The operation member  76  also includes an engaging pawl  82  whose position is held by the pivot member main body  75  for satisfactory forward and backward linear movement. The unlock operation member  76  also includes a bent portion  83  to catch a finger at the distal end. A first stopper surface  109  serving as a first stopper portion formed by a step is provided on the inner surface of the engaging pawl  82  of the operation member  76 . The unlock operation member  76  includes, on the proximal end side, a projection  80  that has a second stopper surface  79  serving as the first stopper portion formed by one side surface and projects substantially backward. 
         [0066]    The pivot member main body  75  has an opening  84  serving as an unloaded hole to insert the shaft member  27  with washer to a substantially center of it, as shown in  FIGS. 7 and 8 . The pivot member main body  75  includes a first engaging pawl  87  that engages with a first engaged pawl  85  of the shield plate  4  shown in  FIG. 10 , and a second engaging pawl  88  that engages with a second engaged pawl  86  serving as the second stopped portion of the shield plate  4 . Note that the moving-side engaging pawl  82  that linearly moves forward and backward forms part of the second engaging pawl  88 . In addition, an engaged projection  91  to be guided by the engaging opening  55  of the shield base  24  is disposed on the inner surface of the pivot member main body  75 . 
         [0067]    The shield plate  4  is provided with a guided projecting wall  92  that runs in a substantially semicircular shape between the first engaged pawl  85  and the second engaged pawl  86 , as shown in  FIG. 10 . Since a missing portion  90  exists near the second engaged pawl  86 , the guided projecting wall  92  is formed from a first guided projecting wall  92   a  and a second guided projecting wall  92   b . The pivot member main body  75  shown in  FIGS. 7 and 8  is provided with a guide projecting wall  93  that guides the guided projecting wall  92  by its outer surface. A repulsive coil spring  94  serving as an elastic biasing means is interposed between the pivot member main body  75  and the unlock operation member  76 , as shown in  FIG. 8 . First and second repulsive coil springs  95  and  96  each serving as an elastic biasing means are interposed between the shield base  24  and the pivot member main body  75 . More specifically, the first repulsive coil spring  95  is interposed between the first spring engaging convex portion  56  and a first spring engaging concave portion  97  of the pivot member main body  75 . The second repulsive coil spring  96  is interposed between the second spring engaging convex portion  57  and a second spring engaging concave portion  98  of the pivot member main body  75 . 
         [0068]    A corrugated clicking tooth portion  101  formed to face the side of the opening  84  is disposed on the pivot member main body  75  shown in  FIGS. 7 and 8 . A clicking tooth portion  102  that can engage with the clicking tooth portion  101  is disposed on the inner surface of the shield plate  4  shown in  FIG. 10 . A position holding projection  104  capable of moving forward and backward substantially along a followed surface  70  formed from the rear end surface on the opposite side of the followed surface  71  of the projecting wall  72  of the shield base  24  is disposed on the inner surface of the shield plate  4 . In addition, a projection  105  serving as a second following surface capable of moving forward and backward substantially along the followed surface  71  of the projecting wall  72  of the shield base  24  shown in  FIGS. 6 to 8  is disposed on the inner surface of the shield plate  4 . 
         [0069]    The shaft member  27  with washer includes a shaft portion  106 , a washer portion  107  integrated with the shaft portion  106 , and a center opening  108  extending through the whole shaft member  27  including the shaft portion  106  and the washer portion  107 , as shown in  FIGS. 8 and 9 . The outer surface of the shaft portion  106  is provided with a pair of substantially front and back convex followed surfaces  111  and  112  substantially facing each other. The projections  44   a  and  44   b  of the shaft member  27  with washer are disposed on the inner surfaces of the convex followed surfaces  111  and  112  respectively. Since the diameter of the washer portion  107  gradually decreases clockwise in  FIG. 8 , a step portion  113  serving as a third stopper portion is formed on the outer surface of the washer portion  107 . For this reason, the abutted portion  113  serving as a stopper surface is formed by the step portion. On the other hand, an abutting portion  114  serving as the third stopper portion disposed to face the first engaged pawl  85  at one end of the guided projecting wall  92  is formed on the shield plate  4  shown in  FIG. 10 . When the shield plate  4  that has already risen to some extent is set in the uppermost state (in other words, a state in which the shield plate has risen by 80°) by raising the chin guard  6 , the abutting portion  114  abuts against the abutted portion  113  to prevent further rise of the shield plate  4 . 
         [0070]    3. Operation of Chin Guard Support Mechanism 
         [0071]    The shield plate  4  can take at least each of: 
         [0072]    (a) the lowermost state shown in  FIGS. 1 ,  3 , and  11 , 
         [0073]    (b) a state in which the shield plate  4  has risen by 1° shown in  FIG. 13 , 
         [0074]    (c) a state in which the shield plate  4  has risen by 2° shown in  FIG. 14 , 
         [0075]    (d) a state in which the shield plate  4  has risen by 4° shown in  FIG. 15 , 
         [0076]    (e) a state in which the shield plate  4  has risen by 8° shown in  FIG. 16 , 
         [0077]    (f) a state in which the shield plate  4  has risen by 16° shown in  FIG. 17 , 
         [0078]    (g) a state in which the shield plate  4  has risen by 48° shown in  FIG. 12  (in other words, the uppermost state of the shield plate  4  in the lowermost state of the chin guard  6 ), and 
         [0079]    (h) the uppermost state in which the shield plate  4  has risen by 80° shown in  FIGS. 2 ,  4 , and  18 . 
         [0080]    When the helmet wearer or the like performs an appropriate operation, the shield plate  4  can continuously rise from the state described in (a) to the state described in (h). In addition, when the helmet wearer or the like performs an appropriate operation, the shield plate  4  can continuously lower from the state described in (h) to the state described in (a). 
         [0081]    The chin guard  6  can take at least each of: 
         [0082]    (i) the lowermost state shown in  FIGS. 1 ,  3 ,  9 ,  11 , and  12 , 
         [0083]    (j) a state in which the chin guard  6  has risen by 1° shown in  FIG. 13 , 
         [0084]    (k) a state in which the chin guard  6  has risen by 2° shown in  FIG. 14 , 
         [0085]    (l) a state in which the chin guard  6  has risen by 4° shown in  FIG. 15 , 
         [0086]    (m) a state in which the chin guard  6  has risen by 8° shown in  FIG. 16 , 
         [0087]    (n) a state in which the chin guard  6  has risen by 16° shown in  FIG. 17 , and 
         [0088]    (o) a state in which the chin guard  6  has risen by 80° shown in  FIGS. 2 ,  4 , and  18 . 
         [0089]    When the helmet wearer or the like performs an appropriate operation, the chin guard  6  can continuously rise from the state described in (i) to the state described in (o). In addition, when the helmet wearer or the like performs an appropriate operation, the chin guard  6  can continuously lower from the state described in (o) to the state described in (i). 
         [0090]    As described above, the shield plate  4  and the chin guard  6  will be described below sequentially in: 
         [0091]    (A) a state in which each of the shield plate  4  and the chin guard  6  is at the lowermost position, as shown in  FIGS. 1 ,  3 ,  9 , and  11 , 
         [0092]    (B) a state in which each of the shield plate  4  and the chin guard  6  has risen by 1°, as shown in  FIG. 13 , 
         [0093]    (C) a state in which each of the shield plate  4  and the chin guard  6  has risen by 2°, as shown in  FIG. 14 , 
         [0094]    (D) a state in which each of the shield plate  4  and the chin guard  6  has risen by 4°, as shown in  FIG. 15 , 
         [0095]    (E) a state in which each of the shield plate  4  and the chin guard  6  has risen by 8°, as shown in  FIG. 16 , 
         [0096]    (F) a state in which each of the shield plate  4  and the chin guard  6  has risen by 16°, as shown in  FIG. 17 , 
         [0097]    (G) a state in which each of the shield plate  4  and the chin guard  6  has risen by 80°, as shown in  FIGS. 2 ,  4 , and  18 , and 
         [0098]    (H) a state in which the chin guard  6  is located at the lowermost position, and only the shield plate  4  has risen by 48°, as shown in  FIG. 12  with reference to the accompanying drawings. 
         [0099]    (A) State in which Shield Plate  4  and Chin Guard  6  are at Lowermost Position 
         [0100]    In the state described in (A), a lock means (not shown) such as a lock pawl of the chin guard  6  engages with the lock pin  19  of the main cap body  5  shown in  FIGS. 2 ,  4 , and  5 , thereby holding the chin guard  6  at the lowermost position shown in  FIGS. 1 ,  3 ,  9 , and  11 . In this state, the convex annular followed surface  111  formed from the outer surface of the shaft portion  106  of the shaft member  27  with washer partially contacts the concave annular following surface  65  formed from the edge of the opening  66  of the shield base  24 , as indicated by the alternate long and short dashed line in  FIG. 13 . More specifically, the convex annular followed surface  111  includes a followed surface main body portion  123  having a substantially circular shape when viewed two-dimensionally, and a pair of substantially mountain-shaped convex followed surface portions  124  and  125  projecting from the main body portion  123  outward to face each other, as shown in  FIGS. 13A and 13B . The concave annular following surface  65  includes a concave following surface portion  126  arranged to fit on, engage with, or contact the convex followed surface portion  124  and having a substantial mountain shape substantially corresponding to the convex followed surface portion  124 , a concave following surface portion  127  arranged to contact the convex followed surface portion  125  and configured to be much longer in the circumferential direction (in other words, wider) than the convex followed surface portion  125 , and a following surface portion  131  having a bent shape and arranged on one side between the pair of concave following surface portions  126  and  127  to contact the followed surface main body portion  123  having a substantially circular shape. Note that the total of three portions, that is the concave following surface portions  126  and  127  and the following surface portion  131  having the bent shape are arranged at sufficient distances. 
         [0101]    When the chin guard  6  is located at the lowermost position indicated by the alternate long and short dashed line in  FIG. 13 , the convex annular followed surface  111  contacts the concave following surface portion  126  at three portions described in (i) to (iii), as shown in  FIG. 13A : 
         [0102]    (i) the surfaces contact each other as the peripheral surface of the convex followed surface portion  124  relatively engages with a region including the peripheral surface of the concave following surface portion  126  and a vicinity thereof; 
         [0103]    (ii) the surfaces contact each other as the peripheral surface of the convex followed surface portion  125  relatively contacts with a region including the peripheral surface of the concave following surface portion  127  long in the circumferential direction and a vicinity thereof; and 
         [0104]    (iii) the surfaces contact each other as a portion  123   a  on one side out of the followed surface main body portion  123  having a substantially circular shape between the convex followed surface portions  124  and  125  contacts the following surface portion  131  having a bent shape. 
         [0105]    Hence, the shaft member  27  with washer holds the opening  66  at a predetermined position by contacts at the three portions (to be referred to as “the contacts at the three portions” hereinafter). Note that the contacts at the three portions are substantially always done independently of the up positions of the chin guard  6  and the shield plate  4 . 
         [0106]    The position of the shield plate  4  in the lowering direction is regulated by a rim member (not shown) such as rim rubber extending along the upper end of the chin cover  6   a  of the chin guard  6 . The position of the shield plate  4  in the rising direction is regulated by engaging the clicking tooth portion  102  of the shield plate  4  with the clicking tooth portion  101  of the pivot member main body  75  shown in  FIG. 7 . A lock lever (not shown) can be provided as needed. In this case, the shield plate  4  is locked by operating the lock lever, thereby forcibly preventing the rise of the shield plate  4 . When the lock lever is operated to an unlock state, the shield plate  4  can manually be raised. The shield plate  4  can also manually be raised and lowered while keeping the chin guard  6  held at the lowermost position. 
         [0107]    (B) State in which Shield Plate  4  and Chin Guard  6  have Risen by 1° 
         [0108]    To change the state described in (A) indicated by the alternate long and short dashed line in  FIG. 13  (in other words, the state shown in  FIG. 13A ) to the state described in (B) indicated by the alternate long and two short dashed line in  FIG. 13  (in other words, the state shown in  FIG. 13B ), the unlock operation button  18  shown in  FIG. 2  is pressed substantially downward. With this press operation, the lock means of the chin guard  6  disengages from the lock pin  19  of the main cap body  5 . In addition, the chin guard  6  is manually raised by 1°. For this reason, the opening  66  of the shield base  24  slightly pivots clockwise in  FIG. 13  with respect to the shaft portion  106  of the shaft member  27  with washer. The concave annular following surface  65  of the opening  66  is going to slightly rise with respect to the convex annular followed surface  111  of the shaft portion  106 , and therefore moves obliquely forward as well while slightly rising. In this case, the shield pivot member  25  that is integrally coupled to the chin guard  6  at this point of time moves integrally with the shield base  24 . For this reason, the shield plate  4  located at the position indicated by the alternate long and short dashed line in  FIG. 13  moves substantially integrally with the chin guard  6 , as indicated by the alternate long and two short dashed line in  FIG. 13 . The linear movement of the shaft portion  106  relative to the opening  66  is prevented by the contacts at the three portions. For this reason, each of the chin guard  6  and the shield plate  4  rises from the position indicated by the alternate long and short dashed line in  FIG. 13  to the position indicated by the alternate long and two short dashed line in  FIG. 13 , and also moves forward. 
         [0109]      FIG. 19  illustrates one reference example in which an attachment shaft  121  that is the pivot of the chin guard  6  of the helmet  1  shown in  FIG. 13  is assumed to be set at a fixed position.  FIG. 19  shows a state in which the chin guard  6  has been manually made to pivot by 1° from the lowermost state in the rising direction. Note that when the chin guard  6  pivots by 1°, the shield plate  4  also pivots by 1° in the rising direction, accompanied by the chin guard  6 . In this case, the shield plate  4  simply pivots in the rising direction, like the chin guard  6 . Since especially the inner surface of the upper end of the shield plate  4  comes into contact with a rim member  122  such as rim rubber on the side of the main cap body  5  and rubs, the shield plate  4  and/or the rim member  122  is readily damaged. However, in the embodiment shown in  FIG. 13  and the like, since each of the chin guard  6  and the shield plate  4  not only pivots in the rising direction but also moves forward, as described above, the damage can effectively be prevented. 
         [0110]    (C) State in which Shield Plate  4  and Chin Guard  6  have Risen by 2° 
         [0111]    To change the state described in (B) indicated by the alternate long and two short dashed line in  FIG. 13  (in other words, the alternate long and short dashed line in  FIG. 14 ) to the state described in (C) indicated by the alternate long and two short dashed line in  FIG. 14 , the chin guard  6  is further manually raised by 1°. For this reason, the opening  66  slightly pivots clockwise in  FIG. 13  with respect to the shaft portion  106 , as in the case described in (B). Hence, the convex followed surface portion  124  of the convex annular followed surface  111  is going to slightly disengage from the concave following surface portion  126 . As a result, the shield plate  4  located at the position indicated by the alternate long and two short dashed line in  FIG. 14  further moves substantially integrally with the chin guard  6 , as indicated by the alternate long and short dashed line in  FIG. 14 . The linear movement of the shaft portion  106  relative to the opening  66  is prevented by the contacts at the three portions. For this reason, each of the chin guard  6  and the shield plate  4  rises from the position indicated by the alternate long and short dashed line in  FIG. 14  to the position indicated by the alternate long and two short dashed line in  FIG. 14  and also moves forward. 
         [0112]    (D) State in which Shield Plate  4  and Chin Guard  6  have Risen by 4° 
         [0113]    To change the state described in (C) indicated by the alternate long and two short dashed line in  FIG. 14  (in other words, the alternate long and short dashed line in  FIG. 15 ) to the state described in (D) indicated by the alternate long and two short dashed line in  FIG. 15 , the chin guard  6  is further manually raised by 2°. For this reason, the opening  66  slightly pivots clockwise in  FIG. 14  with respect to the shaft portion  106 , as in the case described in (C). Hence, the convex followed surface portion  124  is going to further slightly disengage from the concave following surface portion  126 . Hence, the shield plate  4  located at the position indicated by the alternate long and short dashed line in  FIG. 15  further moves substantially integrally with the chin guard  6 , as indicated by the alternate long and two short dashed line in  FIG. 15 . The linear movement of the shaft portion  106  relative to the opening  66  is prevented by the contacts at the three portions. For this reason, each of the chin guard  6  and the shield plate  4  rises from the position indicated by the alternate long and short dashed line in  FIG. 15  to the position indicated by the alternate long and two short dashed line in  FIG. 15 , and also moves forward. 
         [0114]    (E) State in which Shield Plate  4  and Chin Guard  6  have Risen by 8° 
         [0115]    To change the state described in (D) indicated by the alternate long and two short dashed line in  FIG. 15  (in other words, the alternate long and short dashed line in  FIG. 16 ) to the state described in (E) indicated by the alternate long and two short dashed line in  FIG. 16 , the chin guard  6  is further manually raised by 4°. For this reason, the opening  66  pivots clockwise in  FIG. 15  to some extent with respect to the shaft portion  106 , as in the case described in (D). Hence, the substantially whole convex followed surface portion  124  is going to disengage from the concave following surface portion  126 . Hence, the shield plate  4  located at the position indicated by the alternate long and short dashed line in  FIG. 16  further moves substantially integrally with the chin guard  6 , as indicated by the alternate long and two short dashed line in  FIG. 16 . The linear movement of the shaft portion  106  relative to the opening  66  is prevented by the contacts at the three portions. For this reason, each of the chin guard  6  and the shield plate  4  rises from the position indicated by the alternate long and short dashed line in  FIG. 16  to the position indicated by the alternate long and two short dashed line in  FIG. 16 , and also moves forward. 
         [0116]    (F) State in which Shield Plate  4  and Chin Guard  6  have Risen by 16° 
         [0117]    To change the state described in (E) indicated by the alternate long and two short dashed line in  FIG. 16  to the state described in (F) indicated by the alternate long and two short dashed line in  FIG. 17 , the chin guard  6  is further manually raised by 8°. For this reason, the opening  66  pivots clockwise in  FIG. 16  to some extent with respect to the shaft portion  106 , as in the case described in (E). Hence, the entire convex followed surface portion  124  wholly disengages relatively from the concave following surface portion  126  and comes into contact with a following surface main body portion  128  having a substantially circular shape. Hence, the shield plate  4  located at the position indicated by the alternate long and two short dashed line in  FIG. 16  moves substantially integrally with the chin guard  6 , as indicated by the alternate long and two short dashed line in  FIG. 17 . The linear movement of the shaft portion  106  relative to the opening  66  is prevented by the contacts at the three portions. For this reason, each of the chin guard  6  and the shield plate  4  rises from the position indicated by the alternate long and two short dashed line in  FIG. 16  to the position indicated by the alternate long and two short dashed line in  FIG. 17 , and also moves forward. 
         [0118]    (G) State in which Shield Plate  4  and Chin Guard  6  have Risen by 80° 
         [0119]    To change the state described in (F) indicated by the alternate long and two short dashed line in  FIG. 17  to the state described in (G) indicated by the alternate long and two short dashed line in  FIG. 18 , the chin guard  6  is further manually raised by 64°. For this reason, the opening  66  largely pivots clockwise in  FIG. 17  with respect to the shaft portion  106 , as in the case described in (F). Hence, the convex followed surface portion  124  relatively moves counterclockwise in  FIG. 17  along the following surface main body portion  128  having a substantially circular shape. Hence, the shield plate  4  located at the position indicated by the alternate long and two short dashed line in  FIG. 17  moves substantially integrally with the chin guard  6 , as indicated by the alternate long and two short dashed line in  FIG. 18 . The linear movement of the shaft portion  106  relative to the opening  66  is prevented by the contacts at the three portions. For this reason, each of the chin guard  6  and the shield plate  4  rises from the position indicated by the alternate long and two short dashed line in  FIG. 17  to the position indicated by the alternate long and two short dashed line in  FIG. 18  without substantially moving forward. Note that the position indicated by the alternate long and two short dashed line in  FIG. 18  is the uppermost position for each of the chin guard  6  and the shield plate  4 . In this case, the rise of the chin guard  6  from the uppermost position is prevented as the tubular projection  33  of the shield base  24  climbs over the triangular prism-shaped projection  35  of the support plate  21  and then abuts against the stopper projection  36 . When the shield plate  4  has come to the uppermost position, further rise of the shield plate  4  is prevented as abutting portion  114  of the shield plate  4  abuts against the stopper surface  113  of the shaft member  27  with washer. 
         [0120]    (H) State in which Chin Guard  6  is at Lowermost Position, and Only Shield Plate  4  has Risen by 48° 
         [0121]    In the state described in (H), the chin guard  6  is held at the lowermost position shown in  FIG. 12 , as in the case described in (A). When the shield plate  4  is raised from the position indicated by the solid line in  FIG. 11  and the alternate long and short dashed line in  FIG. 13  to the position indicated by the solid line in  FIG. 12 , the shield plate  4  comes to the uppermost position when the chin guard  6  is held at the lowermost position shown in  FIG. 12 . In this case, the first and second engaged pawls  85  and  86  of the shield plate  4  are guided by the first and second engaging pawls  87  and  88  of the pivot member main body  75  of the shield pivot member  25  and the engaging pawl  82  of the unlock operation member  76 . In addition, since the following projection  105  of the shield plate  4  moves upward from the lower side along the convex followed surface  71  of the shield base  24 , the shield plate  4  not only simply rises but also slightly moves forward. This prevents the inner surface of the shield plate  4  from unnecessarily contacting the outer surface of the main cap body  5 . When the shield plate  4  has risen by 48° to the up position while keeping the chin guard  6  held at the lowermost position, further rise of the shield plate  4  is prevented by a first abutment in which a stopped front end portion  86   a  serving as a first stopped portion of the second engaged pawl  86  of the shield plate  4  abuts against the first stopper surface  109  serving as the first stopper portion of the unlock operation member  76 . When the shield plate  4  has risen by 48° to the up position, as described above, further rise of the shield plate  4  is also prevented by a second abutment in which a stopped front end face  110  serving as the first stopped portion of the second guided projecting wall  92   b  of the shield plate  4  abuts against the second stopper surface  79  serving as a first stopper portion. In this case, the shield plate  4  can be configured such that its rise is prevented mainly by at least one (for example, the first abutment) of the first abutment and the second abutment. Note that when the shield plate  4  is detached by moving the unlock operation member  76  forward, the first stopper surface  109  moves forward to a position not to abut against the stopped front end portion  86   a.    
         [0122]    The pivot angle (in other words, the second predetermined angle) of the chin guard  6  from the lowermost position to the uppermost position is 80°, as shown in  FIGS. 2 ,  4 , and  18 . The pivot angle (in other words, the first predetermined angle) of the shield plate  4  to the uppermost position when only the shield plate  4  pivots from the lowermost position while keeping the chin guard  6  held at the lowermost position is 48°, as shown in  FIG. 12 . Hence, if the chin guard  6  pivots to the uppermost position while keeping the shield plate  4  held at the uppermost position, the shield plate  4  may pivot by 128° from the lowermost position. However, since the abutting portion  114  of the shield plate  4  abuts against the stopper surface  113  of the shaft member  27  with washer, as described above, the uppermost position of the shield plate  4  is regulated to the position raised by 80° from the lowermost position. For this reason, even when the chin guard  6  is raised while keeping the shield plate  4  raised, the uppermost position of the shield plate  4  is substantially the same as the uppermost position when the chin guard  6  and the shield plate  4  are raised integrally. That is, let α be the pivot angle of the chin guard  6  from the lowermost position to the uppermost position. When α ranges from 0° to 32°, the maximum value of the pivot angle of the shield plate  4  from the lowermost position to the uppermost position is 48°+α. When α ranges from 32° to 80°, the maximum value of the pivot angle of the shield plate  4  from the lowermost position to the uppermost position is 80°. 
         [0123]    Having described a specific preferred embodiment of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. 
         [0124]    For example, in the above-described embodiment, the annular followed surface  111  is formed into a convex shape, and the annular following surface  65  is formed into a concave shape. However, conversely, the annular followed surface  111  may be formed into a concave shape, and the annular following surface  65  may be formed into a convex shape. 
         [0125]    In the above-described embodiment, the concave annular following surface  65  is formed from the edge of the opening  66 . However, the concave annular following surface  65  need not always be formed from the edge of the opening  66 . The concave annular following surface  65  may be formed from the edge of a recess, or the edge of a concave portion partially including a recess and an opening. 
         [0126]    In the above-described embodiment, each of the annular followed surface  111  and the annular following surface  65  is formed into a complete annular shape. However, each of the annular followed surface  111  and the annular following surface  65  need only be formed into a substantially annular shape as long as the contacts at the three portions are satisfactorily done. “The annular following surface  65  follows the annular followed surface  111 ” in the text means that the annular following surface  65  formed into a substantially annular shape substantially moves (for example, substantially pivots) in partial contact with the annular followed surface  111  formed into a substantially annular shape while keeping the same contact relationship as that of a cam follower and a cam. Hence, the combination of the following surface  65  or  105  and the followed surface  111  or  71  is substantially the same as the relationship of a cam follower and a cam. 
         [0127]    In the above-described embodiment, the pivot angle (in other words, the second predetermined angle) of each of the shield plate  4  and the chin guard  6  from the lowermost position to the uppermost position is 80°. However, the pivot angle need not always be 80°. Each pivot angle preferably ranges from 60° to 100° from the viewpoint of practicality, and more preferably ranges from 70° to 90°. The shield plate  4  and the chin guard  6  need not always have a substantially same pivot angle each other. 
         [0128]    In the above-described embodiment, the pivot angle (in other words, the first predetermined angle) of the shield plate  4  to the uppermost position when only the shield plate  4  pivots from the lowermost position while keeping the chin guard  6  held at the lowermost position is 48°. However, the pivot angle need not always be 48°. The pivot angle preferably ranges from 36° to 60° and more preferably ranges from 40° to 56°, from the viewpoint of practicality.