Abstract:
An airbag device, comprising: a gas generation device that is operable to generate gas; and an airbag that includes: a first chamber portion that is disposed at a vehicle front side of a vehicle seat on which a vehicle occupant sits, the first chamber portion being inflated due to gas generated by the gas generation device being supplied into the first chamber portion, a second chamber portion that is inflated due to gas generated by the gas generation device being supplied into the second chamber portion and that is disposed adjacent to the first chamber portion in a vehicle width direction, and a connection portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-225863 filed on Nov. 18, 2015, the disclosure of which is incorporated by reference herein. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present disclosure relates to an airbag device and an airbag fabrication method. 
         [0004]    Related Art 
         [0005]    Japanese Patent Application Laid-Open (JP-A) No. 2013-14176 discloses an airbag device that is accommodated in a center pad of a steering wheel. This airbag device is equipped with an airbag bag body (an airbag) that, when there is a collision of the vehicle, is expanded (inflated) toward the side thereof at which a vehicle occupant is sitting on a driver seat. The airbag bag body is provided with a first chamber that protects the head portion of the vehicle occupant, and a first projection portion and a second projection portion are formed at each of two vehicle width direction edges of the first chamber. The first and second projection portions can be inflated and expanded towards the vehicle rear side relative to the first chamber. If a collision load is applied to the vehicle by a front collision, the head portion of the vehicle occupant is restrained and protected by the first chamber of the airbag bag body. If a collision load is applied to the vehicle by a side face collision, the head portion of the vehicle occupant is restrained and protected by the first projection portion and second projection portion of the airbag bag body. 
         [0006]    Thus, with the airbag device recited in JP-A No. 2013-14176, impacts occurring at the head portion of the vehicle occupant may be moderated in different collision modes. 
         [0007]    However, with an airbag device including an airbag that is expanded at the front side of a vehicle occupant sitting on a seat, it is desirable both to be able to restrain the head portion of a vehicle occupant when a collision load is applied to the vehicle from the vehicle front side and to be able to restrain the head portion of the vehicle occupant when a collision load is applied to the vehicle from a vehicle diagonal front side. 
       SUMMARY 
       [0008]    In consideration of the circumstances described above, a first object of the present disclosure is to provide an airbag device that may restrain the head portion of a vehicle occupant when a collision load is applied to a vehicle from a vehicle diagonal front side, and a second object of the present disclosure is to provide an airbag fabrication method that enables restraint of the head portion of a vehicle occupant when a collision load is applied to a vehicle from a vehicle diagonal front side. 
         [0009]    An airbag device of a first aspect, comprising: a gas generation device that is operable to generate gas; and an airbag that includes: a first chamber portion that is disposed at a vehicle front side of a vehicle seat on which a vehicle occupant sits, the first chamber portion being inflated due to gas generated by the gas generation device being supplied into the first chamber portion, a second chamber portion that is inflated due to gas generated by the gas generation device being supplied into the second chamber portion and that is disposed adjacent to the first chamber portion in a vehicle width direction, a boundary between the inflated first chamber portion and the second chamber portion being disposed so as to be offset in the vehicle width direction relative to a halfway line that divides the vehicle seat into equal halves in the vehicle width direction in plan view, and a connection portion that links regions at a vehicle upper side of a plurality of the inflated chamber portions together in the vehicle width direction. 
         [0010]    According to the airbag device of the first aspect, when the gas generated by the gas generation device is supplied into the first chamber portion and second chamber portion of the airbag, the first chamber portion and second chamber portion are inflated at the front side of a vehicle occupant sitting on the vehicle seat. In a state subsequent to the inflation of the first chamber portion and the second chamber portion, the boundary between the first chamber portion and the second chamber portion is disposed so as to be offset in the vehicle width direction relative to the halfway line that divides the vehicle seat in half in the vehicle width direction. Hence, if the head portion of a vehicle occupant sitting on the vehicle seat is moved diagonally toward the front side, toward the side of a collision, by a collision load being applied to the vehicle from a vehicle diagonal front side, the head portion of the vehicle occupant is disposed between the first chamber portion and the second chamber portion, and the head portion of the vehicle occupant pushes the second chamber portion in a direction away from the first chamber portion. In this situation, in the present disclosure according to the first aspect, the regions at the vehicle upper sides of the plural chamber portions are linked together via the connection portion. Therefore, even when the head portion of the vehicle occupant that is disposed between the first chamber portion and the second chamber portion pushes the second chamber portion in the direction away from the first chamber portion, a gap between the first chamber portion and the second chamber portion is resistant to opening up. Therefore, the head portion of the vehicle occupant may be restrained. 
         [0011]    The airbag device of a second aspect, wherein: the airbag includes a pair of the second chamber portions, the pair of the second chamber portions respectively being disposed at one side and another side of the first chamber portion in the vehicle width direction; and the connection portion links together the first chamber portion and the pair of the second chamber portions or links together one of the pair of the second chamber portions and the other of the pair of the second chamber portions. 
         [0012]    According to the airbag device of the second aspect, if the head portion of a vehicle occupant sitting on the vehicle seat is moved diagonally toward the front-right side by a collision load being applied to the vehicle diagonally from the vehicle front-right side, the head portion of the vehicle occupant moves to between the first chamber portion and the second chamber portion at the one side. If the head portion of the vehicle occupant sitting on the vehicle seat is moved diagonally toward the front-left side by a collision load being applied to the vehicle diagonally from the vehicle front-left side, the head portion of the vehicle occupant moves to between the first chamber portion and the second chamber portion at the another side. Consequently, rotating of the head portion of the vehicle occupant may be suppressed while the head portion of the vehicle occupant is being restrained. 
         [0013]    The airbag device of a third aspect, wherein, in an inflated state of the airbag, an end portion at a vehicle rear side of the first chamber portion is disposed at a vehicle front side relative to an end portion at a vehicle rear side of the second chamber portion. 
         [0014]    According to the airbag device of the third aspect, if the head portion of a vehicle occupant sitting on the vehicle seat is moved diagonally toward the front side by a collision load being applied to the vehicle from a vehicle diagonal front side, the head portion of the occupant moves to between the first chamber portion and the second chamber portion while pushing the end portion at the vehicle rear side of the second chamber portion in the direction away from the first chamber portion (pushing wider the gap between the first chamber portion and the second chamber portion). Thus, in the present disclosure according to the third aspect, it may be made easier for the head portion of the vehicle occupant to move to between the first chamber portion and the second chamber portion. 
         [0015]    An airbag fabrication method of a fourth aspect to fabricate the airbag of the airbag device according to the first aspect, the method employing a first sheet member and a second sheet member, wherein the first sheet member is formed in a sheet shape and includes a front side first extension portion and a front side second extension portion that structure regions at one side and another side in the vehicle width direction of a region at a vehicle front side of the inflated airbag, a gas generation device insertion hole at which a portion of the gas generation device is inserted being formed at a boundary between the front side first extension portion and the front side second extension portion, and wherein the second sheet member is formed in a sheet shape and includes a rear side first extension portion and a rear side second extension portion that structure regions at one side and another side in the vehicle width direction of a region at a vehicle rear side of the inflated airbag, the method comprising: forming the first chamber portion by joining an outer periphery portion of the front side first extension portion to an outer periphery portion of the rear side first extension portion; forming the second chamber portion by joining an outer periphery portion of the front side second extension portion to an outer periphery portion of the rear side second extension portion; and joining one or more of the connection portion to a plurality of the chamber portions. 
         [0016]    According to the airbag fabrication method of the fourth aspect, the first chamber portion of the airbag is formed by the outer periphery portion of the front side first extension portion of the first sheet member and the outer periphery portion of the rear side first extension portion of the second sheet member being joined together. the second chamber portion of the airbag is formed by the outer periphery portion of the front side second extension portion of the first sheet member and the outer periphery portion of the rear side second extension portion of the second sheet member being joined together. The single or plural connection portion is/are joined to the plural chamber portions of the airbag. Through three steps described above, an airbag may be provided that may allow the head portion of a vehicle occupant moving diagonally toward the front side during a collision of a vehicle to move to between the first chamber portion and the second chamber portion and that may restrain the head portion. 
         [0017]    An airbag fabrication method of a fifth aspect to fabricate the airbag of the airbag device according to the second aspect, the method employing a first sheet member, a second sheet member and a third sheet member, wherein the first sheet member is formed in a sheet shape and includes a front side first extension portion and a front side second extension portion that structure regions at one side and another side in the vehicle width direction of a region at a vehicle front side of the inflated airbag, a gas generation device insertion hole at which a portion of the gas generation device is inserted being formed at a boundary between the front side first extension portion and the front side second extension portion, wherein the second sheet member is formed in a sheet shape and includes a rear-left side first extension portion and a rear-left side second extension portion that structure a region at a vehicle rear side, and at one side in the vehicle width direction, of the inflated airbag, and wherein the third sheet member s formed in a sheet shape and includes a rear-right side first extension portion and a rear-right side second extension portion that structure a region at a vehicle rear side, and at another side in the vehicle width direction, of the inflated airbag, the method comprising: forming the second chamber portion at the one side of the first chamber portion by joining an outer periphery portion of the front side first extension portion to an outer periphery portion of the rear-left side first extension portion; forming the second chamber portion at the another side of the first chamber portion by joining an outer periphery portion of the front side second extension portion to an outer periphery portion of the rear-right side first extension portion; forming the first chamber portion by joining an outer periphery portion of the rear-left side second extension portion to an outer periphery portion of the rear-right side second extension portion; and joining one or more of the connection portions to a plurality of the chamber portions. 
         [0018]    According to the airbag fabrication method of the fifth aspect, the second chamber portion at the one side of the airbag is formed by the outer periphery portion of the front side first extension portion of the first sheet member and the outer periphery portion of the rear-left side first extension portion of the second sheet member being joined together. The second chamber portion at the another side of the airbag is formed by the outer periphery portion of the front side second extension portion of the first sheet member and the outer periphery portion of the rear-right side first extension portion of the third sheet member being joined together. The first chamber portion of the airbag is formed by the outer periphery portion of the rear-left side second extension portion of the second sheet member and the outer periphery portion of the rear-right side second extension portion of the third sheet member being joined together. The single or plural connection portion is/are joined to the plural chamber portions of the airbag. Through four steps described above, an airbag may be provided that may allow the head portion of a vehicle occupant moving diagonally toward the front-right or front-left side during a collision of a vehicle to move to between the first chamber portion and one of the second chamber portions and that may restrain the head portion. 
         [0019]    The airbag device relating to the present disclosure has an excellent effect in that the airbag device may restrain the head portion of a vehicle occupant when a collision load is applied to a vehicle from a vehicle diagonal front side. The airbag fabrication method relating to the present disclosure has an excellent effect in that the method may provide an airbag that may restrain the head portion of a vehicle occupant when a collision load is applied to a vehicle from a vehicle diagonal front side. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
           [0021]      FIG. 1  is a plan view showing a state in which an airbag device in accordance with a first exemplary embodiment has been operated. 
           [0022]      FIG. 2A  is a front view in which the airbag device in accordance with the first exemplary embodiment is seen from a driver seat side thereof. 
           [0023]      FIG. 2B  is a sectional diagram showing a section of an airbag cut along line  2 B- 2 B shown in  FIG. 2A . 
           [0024]      FIG. 3  is a side view showing a vehicle occupant and the airbag in a completed expansion state. 
           [0025]      FIG. 4A  is a plan view, corresponding to  FIG. 1 , showing a state in which the head of the vehicle occupant starts to abut against a center chamber portion of the airbag. 
           [0026]      FIG. 4B  is a plan view, corresponding to  FIG. 1 , showing a state in which the head of the vehicle occupant starts to abut against a right side chamber portion of the airbag. 
           [0027]      FIG. 5  is a plan view, corresponding to  FIG. 1 , showing a state in which the head of the vehicle occupant has moved to between the center chamber portion and the right side chamber portion of the airbag. 
           [0028]      FIG. 6A  is a front view in which an airbag device in accordance with a second exemplary embodiment is seen from the driver seat side thereof. 
           [0029]      FIG. 6B  is a sectional diagram showing a section of an airbag cut along line  6 B- 6 B shown in  FIG. 6A . 
           [0030]      FIG. 7A  is a plan view showing a member that structures a portion of the airbag in accordance with the first exemplary embodiment, showing a first sheet member. 
           [0031]      FIG. 7B  is a plan view showing a member that structures a portion of the airbag in accordance with the first exemplary embodiment, showing a second sheet member. 
           [0032]      FIG. 7C  is a plan view showing a member that structures a portion of the airbag in accordance with the first exemplary embodiment, showing a third sheet member. 
           [0033]      FIG. 8  is a sectional diagram for describing joining states of the members shown in  FIG. 7A  to  FIG. 7C . 
           [0034]      FIG. 9A  is a plan view showing a member that structures a portion of the airbag in accordance with the second exemplary embodiment, showing a first sheet member. 
           [0035]      FIG. 9B  is a plan view showing a member that structures a portion of the airbag in accordance with the second exemplary embodiment, showing a second sheet member. 
           [0036]      FIG. 9C  is a plan view showing a member that structures a portion of the airbag in accordance with the second exemplary embodiment, showing a third sheet member. 
           [0037]      FIG. 10  is a sectional diagram for describing joining states of the members shown in  FIG. 9A  to  FIG. 9C . 
           [0038]      FIG. 11  is a plan view showing an airbag device in accordance with a third exemplary embodiment. 
           [0039]      FIG. 12  is a plan view showing an airbag device in accordance with a fourth exemplary embodiment and an airbag device in accordance with a fifth exemplary embodiment. 
           [0040]      FIG. 13  is a sectional diagram for describing joining states of a first sheet member and second sheet member that structure portions of an airbag shown in  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    Airbag Device According to First Exemplary Embodiment 
         [0042]    An airbag device according to a first exemplary embodiment of the present disclosure is described using  FIG. 1  and  FIG. 2 . The arrow FR, arrow UP, arrow LH and arrow RH that are shown in the drawings indicate, respectively, a forward direction (progress direction), an upward direction, a leftward direction and a rightward direction of a vehicle. Hereinafter, where descriptions are given simply indicating the directions front and rear, left and right, and up and down, unless specifically stated otherwise, these indicate front and rear in the vehicle front-and-rear direction, left and right in the vehicle left-and-right direction (the vehicle width direction), and up and down in the vehicle up-and-down direction. 
         [0043]    As shown in  FIG. 1 , an airbag device  10  according to the present exemplary embodiment is provided at a central portion of a steering wheel  12  that is disposed at the front side of a driver seat. A center pad, which is not shown in the drawings, is provided at the central portion of the steering wheel  12 . The center pad does not rotationally displaced when the steering wheel  12  is operated (i.e., does not turn together with the steering wheel  12 ). The airbag device  10  is provided inside the center pad. 
         [0044]    The airbag device  10  is provided with a gas generation device  14  and an airbag  16 . The gas generation device  14  generates gas by operating. The airbag  16  is inflated by the gas produced by the gas generation device  14  being supplied to the interior of the airbag  16 . The airbag device  10  is further provided with an airbag electronic control unit (ECU), which is not shown in the drawings, that activates the gas generation device  14  when a collision (a front collision) of the vehicle is detected. 
         [0045]    The gas generation device  14  includes a gas generating agent and an ignition mechanism that ignites the gas generating agent. Gas at high pressure may be produced in an instant by ignition of the gas generating agent. When the high-pressure gas produced by the gas generation device  14  is supplied into the airbag  16 , the airbag  16  inflates from a stowed state to an expanded state between the steering wheel  12  and a vehicle occupant P. 
         [0046]    The airbag  16  is formed in a bag shape of which a portion at which the gas generation device  14  is connected is open. A state in which the airbag  16  is folded up into a predetermined shape and stowed in the center pad at the central portion of the steering wheel  12  is referred to as the “stowed state”. A state in which the airbag  16  has been inflated to a predetermined shape is referred to as a “completed expansion state”. 
         [0047]    The airbag  16  in the completed expansion state is shown in  FIG. 1 ,  FIG. 2A ,  FIG. 2B  and  FIG. 3 . As shown in these drawings, the airbag  16  is provided with a center chamber portion  18  that serves as a first chamber portion. The center chamber portion  18  is disposed facing the head H of a vehicle occupant P sitting on a vehicle seat  11  (the driver seat) in the vehicle front-and-rear direction. The center chamber portion  18  is formed to be symmetrical in the vehicle width direction about a halfway line L that divides the vehicle seat  11  into equal halves in the vehicle width direction. In the descriptions below, the “halfway line L that divides the vehicle seat  11  into equal halves in the vehicle width direction” is referred to as the “seat center line L”. 
         [0048]    The airbag  16  is further provided with a left side chamber portion  20  that serves as a second chamber portion and a right side chamber portion  22  that also serves as a second chamber portion. The left side chamber portion  20  is disposed adjacent to the center chamber portion  18  in the vehicle width direction, at the left side of the center chamber portion  18 . The right side chamber portion  22  is disposed adjacent to the center chamber portion  18  in the vehicle width direction, at the right side of the center chamber portion  18 . The left side chamber portion  20  and the right side chamber portion  22  are formed to be symmetrical in the vehicle width direction about the seat center line L. 
         [0049]    In the present exemplary embodiment, a rear end portion  18 A of the center chamber portion  18 , a rear end portion  20 A of the left side chamber portion  20 , and a rear end portion  22 A of the right side chamber portion  22  are formed in protruding shapes towards the vehicle rear side in a vehicle plan view, and are gently curved. In a sectional view in which the airbag  16  is cut along the vehicle width direction and the front-and-rear direction, points disposed at the vehicle rear side of the rear end portion  18 A of the center chamber portion  18 , the rear end portion  20 A of the left side chamber portion  20  and the rear end portion  22 A of the right side chamber portion  22  are referred to as protrusion direction apexes  18 B,  20 B and  22 B. The protrusion direction apex  18 B of the center chamber portion  18 , the protrusion direction apex  20 B of the left side chamber portion  20  and the protrusion direction apex  22 B of the right side chamber portion  22  are disposed at the same position in the front-and-rear direction. 
         [0050]    A left side slit  24  that opens to the rear side is formed at a boundary between the center chamber portion  18  and the left side chamber portion  20 , and a right side slit  26  that opens to the rear side is formed at a boundary between the center chamber portion  18  and the right side chamber portion  22 . The left side slit  24  and the right side slit  26  are disposed so as to be offset to the left side and the right side, respectively, relative to the seat center line L. In the present exemplary embodiment, a dimension D 1  from the protrusion direction apex  20 B of the left side chamber portion  20  to a terminal end  24 A (front end) of the left side slit  24  is set to a dimension that is larger than a distance H 4  from a front face H 1  of the head H of the vehicle occupant P to a center of gravity H 2  of the head H. A dimension D 2  from the protrusion direction apex  22 B of the right side chamber portion  22  to a terminal end  26 A (front end) of the right side slit  26  is also set to a dimension that is larger than the distance H 4  from the front face H 1  of the head H of the vehicle occupant P to the center of gravity H 2  of the head H. A distance that is used as the distance H 4  from the front face H 1  to the center of gravity H 2  of the head H of the vehicle occupant P is the distance from the front face (the apex of the nose) to the center of gravity of the head of an AM50 dummy used for crash testing (a dummy representing the average build of an American adult male). 
         [0051]    As shown in  FIG. 1  and  FIG. 2A , an upper end portion of the center chamber portion  18  and an upper end portion of the left side chamber portion  20  are linked together via a left side tether  28  formed in a strap shape that serves as a connection portion, and the upper end portion of the center chamber portion  18  and an upper end portion of the right side chamber portion  22  are linked together via a right side tether  30  formed in a strap shape that also serves as a connection portion. As shown in  FIG. 1 , the left side tether  28  and the right side tether  30  are disposed at the front side relative to the protrusion direction apex  18 B of the center chamber portion  18 , the protrusion direction apex  20 B of the left side chamber portion  20  and the protrusion direction apex  22 B of the right side chamber portion  22 , but at the rear side relative to the terminal ends  24 A and  26 A of the left side slit  24  and right side slit  26 . As shown in  FIG. 3 , the left side tether  28  and the right side tether  30  are disposed at the upper side relative to a head top portion H 3  of the vehicle occupant P sitting on the vehicle seat  11 . A position that is used as the position of the head top portion H 3  of the vehicle occupant P is the position of a head top portion of the head of the AM50 dummy for crash testing, seated on the vehicle seat  11 . 
         [0052]    Operation and Effects of the Present Exemplary Embodiment 
         [0053]    Now, operation and effects of the present exemplary embodiment are described. 
         [0054]    As shown in  FIG. 1  and  FIG. 3 , when a vehicle occupant P sitting on the vehicle seat  11  is driving a vehicle equipped with the airbag device  10  according to the present exemplary embodiment, if the vehicle experiences a front collision at a predetermined speed or above, the gas generation device  14  is operated and the airbag  16  is inflated in an instant. That is, the center chamber portion  18 , left side chamber portion  20  and right side chamber portion  22  of the airbag  16  are inflated in an instant toward the side thereof at which the vehicle occupant P is disposed. Hence, the head H of the vehicle occupant P that is moving toward the front side due to inertia may be arrested by the center chamber portion  18 , left side chamber portion  20  and right side chamber portion  22  of the airbag  16 , and kinetic energy of the vehicle occupant P may be absorbed by the airbag  16 . Then, the gas inside the airbag  16  is gradually released through a vent hole, which is not shown in the drawings. 
         [0055]    When a collision load is applied to the vehicle equipped with the airbag device  10  according to the present exemplary embodiment diagonally from the front-right side, the head H of the vehicle occupant P moves diagonally toward the front-right side, as shown in  FIG. 4A . When a left side region of the head H of the vehicle occupant P abuts against a right side region of the center chamber portion  18 , a moment M 1  in the anticlockwise direction in the vehicle plan view is produced in the head H of the vehicle occupant P. When the head H of the vehicle occupant P moves further diagonally toward the front-right side and, as shown in  FIG. 4B , a right side region of the head H of the vehicle occupant P abuts against a left side region of the right side chamber portion  22 , a moment M 2  in the clockwise direction in the vehicle plan view is produced in the head H of the vehicle occupant P. Thus, moments produced in the head H of the vehicle occupant P may counteract one another, and an injury index of the head H of the vehicle occupant P may be effectively reduced. 
         [0056]    Then, when the head H of the vehicle occupant P moves further diagonally toward the front-right side, as shown in  FIG. 5 , the head H of the vehicle occupant P moves into the right side slit  26  between the center chamber portion  18  and the right side chamber portion  22 . In the state in which the head H of the vehicle occupant P has moved into the right side slit  26 , if the head H of the vehicle occupant P moves further diagonally toward the front-right side, the head H of the vehicle occupant P pushes the right side chamber portion  22  in the direction away from the center chamber portion  18  (i.e., to the right side). In the present exemplary embodiment, the upper end portion of the center chamber portion  18  and the upper end portion of the right side chamber portion  22  are linked together via the right side tether  30 . Therefore, even when the head H of the vehicle occupant P that has moved to between the center chamber portion  18  and the right side chamber portion  22  pushes the right side chamber portion  22  in the direction away from the center chamber portion  18 , the right side slit  26  between the center chamber portion  18  and the right side chamber portion  22  is resistant to opening up. Consequently, rotating of the head H of the vehicle occupant P may be suppressed while the head H of the vehicle occupant P is being restrained. 
         [0057]    If the head H of the vehicle occupant P moves diagonally toward the front-left side due to a collision load being applied diagonally from the front-left side to the vehicle equipped with the airbag device  10  according to the present exemplary embodiment, the head H of the vehicle occupant P moves into the left side slit  24  between the center chamber portion  18  and the left side chamber portion  20  in the same manner. Thus, rotating of the head H of the vehicle occupant P may be suppressed while the head H of the vehicle occupant P is being restrained. 
         [0058]    As shown in  FIG. 3 , in the present exemplary embodiment, the left side tether  28  and the right side tether  30  are disposed at the upper side relative to the head top portion H 3  of the vehicle occupant P sitting on the vehicle seat  11 . Therefore, contact (entanglement) between the head H of the vehicle occupant P and the left side tether  28  and right side tether  30  may be prevented or suppressed. 
         [0059]    As shown in  FIG. 1 , in the present exemplary embodiment, the left side tether  28  and the right side tether  30  are each disposed at the rear side relative to the terminal ends  24 A and  26 A of the left side slit  24  and right side slit  26 . Therefore, when the head H of a vehicle occupant P is moving inside the left side slit  24  or the right side slit  26 , opening up of the left side slit  24  or the right side slit  26  may be effectively suppressed. 
         [0060]    In the present exemplary embodiment, the dimension D 1  from the protrusion direction apex  20 B of the left side chamber portion  20  to the terminal end  24 A (front end) of the left side slit  24  and the dimension D 2  from the protrusion direction apex  22 B of the right side chamber portion  22  to the terminal end  26 A (front end) of the right side slit  26  are set to a dimension larger than the distance H 4  from the front face H 1  of the head H of the vehicle occupant P to the center of gravity H 2  of the head H. Therefore, the head H of a vehicle occupant P that has moved into the left side slit  24  or the right side slit  26  may be inhibited from disengaging from the left side slit  24  or right side slit  26 . 
         [0061]    Airbag Device According to Second Exemplary Embodiment 
         [0062]    An airbag device according to a second exemplary embodiment of the present disclosure is described using  FIG. 6 . Members and portions corresponding with the airbag device  10  according to the first exemplary embodiment described above are assigned the same reference symbols as in the first exemplary embodiment described above and are not described here. 
         [0063]    As shown in  FIG. 6A  and  FIG. 6B , in an airbag device  32  according to the present exemplary embodiment, a face at the vehicle rear side of the center chamber portion  18  in the completed expansion state is disposed at the vehicle front side relative to faces at the vehicle rear side of the left side chamber portion  20  and the right side chamber portion  22  in the completed expansion state, and an upper end portion of the left side chamber portion  20  and an upper end portion of the right side chamber portion  22  are linked together in the vehicle width direction via a tether  34  that serves as the connection portion. 
         [0064]    To describe this in more detail, the protrusion direction apex  18 B of the center chamber portion  18  is disposed at the front side relative to the protrusion direction apex  20 B of the left side chamber portion  20  and the protrusion direction apex  22 B of the right side chamber portion  22 . Therefore, the rear end portion  18 A of the center chamber portion  18  is disposed at the front side relative to the rear end portion  20 A of the left side chamber portion  20  and the protrusion direction apex  22 B of the right side chamber portion  22 . A dimension U 1  in the up-and-down direction of the rear end portion  18 A of the center chamber portion  18  as seen by a vehicle occupant P sitting on the vehicle seat is set to be smaller than dimensions U 2  in the up-and-down direction of the rear end portion  20 A of the left side chamber portion  20  and the rear end portion  22 A of the right side chamber portion  22 . 
         [0065]    In the present exemplary embodiment described above, if the head H of a vehicle occupant P sitting on the vehicle seat moves diagonally toward the front-left or front-right side due to a collision load being applied to the vehicle from a vehicle diagonal front side, the head H of the vehicle occupant P pushes the rear end portion  20 A of the left side chamber portion  20  or the rear end portion  22 A of the right side chamber portion  22  to the side thereof away from the center chamber portion  18 . Hence, the head H of the vehicle occupant P moves into the left side slit  24  or the right side slit  26  while pushing wider the left side slit  24  or the right side slit  26 . 
         [0066]    That is, in the present exemplary embodiment, the head H of the vehicle occupant P may more easily move into the left side slit  24  or the right side slit  26 . 
         [0067]    Airbag Fabrication Method 
         [0068]    Now, a fabrication method of the airbag  16  described above is described. 
         [0069]    As shown in  FIG. 7A  to  FIG. 7C , the airbag  16  that structures a portion of the airbag device  10  according to the first exemplary embodiment described above is fabricated through the following steps, employing a first sheet member  36 , a second sheet member  38  and a third sheet member  40  that are all sheet-shaped and are all formed in predetermined shapes. Below, structures of the first sheet member  36 , the second sheet member  38  and the third sheet member  40  are described, and then the fabrication steps of the airbag  16  are described. 
         [0070]    As shown in  FIG. 7A , the first sheet member  36  is provided with a front side first extension portion  36 A and a front side second extension portion  36 B, which are to structure a region over the left side from the vehicle front side of the airbag  16  and a region over the right side from the vehicle front side in the completed expansion state. The front side first extension portion  36 A and front side second extension portion  36 B are respectively formed in elliptical shapes whose long axis directions are in the vehicle up-and-down direction and are formed to be symmetrical in the left-and-right direction. An up-and-down direction middle portion at the right side of the front side first extension portion  36 A and an up-and-down direction middle portion at the left side of the front side second extension portion  36 B are connected together. A gas generation device insertion hole  36 C is formed at a connection line between the front side first extension portion  36 A and the front side second extension portion  36 B. A gas jetting-out portion of the gas generation device  14  (see  FIG. 1 ), which is a portion at which the gas is jetted out, is to be inserted into the gas generation device insertion hole  36 C. Respective tether joining portions  36 D are formed at upper end portions of the front side first extension portion  36 A and the front side second extension portion  36 B. Each tether joining portion  36 D is formed in a protruding shape toward the upper side. 
         [0071]    As shown in  FIG. 7B , the second sheet member  38  is provided with a rear-left side first extension portion  38 A and a rear-left side second extension portion  38 B, which are to structure a region at the vehicle rear side and left side of the airbag  16  in the completed expansion state. The rear-left side first extension portion  38 A and rear-left side second extension portion  38 B are respectively formed in elliptical shapes whose long axis directions are in the vehicle up-and-down direction and are formed to be symmetrical in the left-and-right direction. An up-and-down direction middle portion at the right side of the rear-left side first extension portion  38 A and an up-and-down direction middle portion at the left side of the rear-left side second extension portion  38 B are connected together. Respective tether joining portions  38 C are formed at upper end portions of the rear-left side first extension portion  38 A and the rear-left side second extension portion  38 B. Each tether joining portion  38 C is formed in a protruding shape toward the upper side. 
         [0072]    As shown in  FIG. 7C , the third sheet member  40  is provided with a rear-right side first extension portion  40 A and a rear-right side second extension portion  40 B, which are to structure a region at the vehicle rear side and right side of the airbag  16  in the completed expansion state. Respective tether joining portions  40 C are formed at upper end portions of the rear-right side first extension portion  40 A and the rear-right side second extension portion  40 B. Each tether joining portion  40 C is formed in a protruding shape toward the upper side. Herein, the shape of the third sheet member  40  is the same as the shape of the second sheet member  38  (an identical member). 
         [0073]    As shown in  FIG. 8 , first, the left side chamber portion  20  is formed by an outer periphery portion of the front side first extension portion  36 A of the first sheet member  36  being joined to an outer periphery portion of the rear-left side first extension portion  38 A of the second sheet member  38  (a first step). Then, the right side chamber portion  22  is formed by an outer periphery portion of the front side second extension portion  36 B of the first sheet member  36  being joined to an outer periphery portion of the rear-right side first extension portion  40 A of the third sheet member  40  (a second step). Then, the center chamber portion  18  is formed by an outer periphery portion of the rear-left side second extension portion  38 B of the second sheet member  38  being joined to an outer periphery portion of the rear-right side second extension portion  40 B of the third sheet member  40  (a third step). The order of the first to third steps described above may be modified. The joining between the respective members may be implemented by sewing, adhesion or the like. 
         [0074]    Then, as shown in  FIG. 1  and  FIG. 7 , one end portion of the left side tether  28  is connected to the tether joining portion  36 D of the front side first extension portion  36 A of the first sheet member  36  and the tether joining portion  38 C of the rear-left side first extension portion  38 A of the second sheet member  38 , and another end portion of the left side tether  28  is joined to the tether joining portion  38 C of the rear-left side second extension portion  38 B of the second sheet member  38  and the tether joining portion  40 C of the rear-right side second extension portion  40 B of the third sheet member  40 . Meanwhile, one end portion of the right side tether  30  is connected to the tether joining portion  36 D of the front side second extension portion  36 B of the first sheet member  36  and the tether joining portion  40 C of the rear-right side first extension portion  40 A of the third sheet member  40 , and another end portion of the right side tether  30  is joined to the tether joining portion  38 C of the rear-left side second extension portion  38 B of the second sheet member  38  and the tether joining portion  40 C of the rear-right side second extension portion  40 B of the third sheet member  40  (a fourth step). Thus, the upper end portion of the center chamber portion  18  and the upper end portion of the left side chamber portion  20  are linked together via the left side tether  28 , and the upper end portion of the center chamber portion  18  and the upper end portion of the right side chamber portion  22  are linked together via the right side tether  30 . 
         [0075]    Thus, the airbag  16  that structures a portion of the airbag device  10  according to the first exemplary embodiment is fabricated through the first to fourth steps described above. 
         [0076]    As shown in  FIG. 9A  to  FIG. 9C  and  FIG. 10 , the airbag  16  that structures a portion of the airbag device  32  according to the second exemplary embodiment described above is similarly fabricated employing the first sheet member  36 , second sheet member  38  and third sheet member  40  that are sheet-shaped and formed in predetermined shapes. In order to obtain the completed expansion state of the airbag  16  according to the second exemplary embodiment, up-and-down and left-and-right dimensions of the rear-left side first extension portion  38 A of the second sheet member  38  are set to be larger than up-and-down and left-and-right dimensions of the rear-left side second extension portion  38 B, and up-and-down and left-and-right dimensions of the rear-right side first extension portion  40 A of the third sheet member  40  are set to be larger than up-and-down and left-and-right dimensions of the rear-right side second extension portion  40 B. The airbag  16  according to the second exemplary embodiment is fabricated through steps corresponding to the first to fourth steps according to the first exemplary embodiment that are described above. 
         [0077]    In the first exemplary embodiment and second exemplary embodiment described above, examples are described in which the present disclosure is applied to the airbag devices  10  and  32  that are disposed at the front side of a driver seat, but the present disclosure is not limited to the above exemplary embodiments. For example, as illustrated in  FIG. 11 , a structure similar to the airbag device  10  according to the first exemplary embodiment may be applied to an airbag device  42  according to a third exemplary embodiment, which is disposed at the front side of an assistant driver seat (a vehicle seat). The airbag device  42  for the assistant driver seat is provided inside an instrument panel  56 . Members and portions of the airbag device  42  for the assistant driver seat that correspond with the airbag device  10  according to the first exemplary embodiment are assigned the same reference symbols as in the first exemplary embodiment. 
         [0078]    In the first to third exemplary embodiments described above, examples are described in which the left side chamber portion  20  and the right side chamber portion  22  are provided at the left side and right side, respectively, of the center chamber portion  18  that is disposed to oppose the head H of a vehicle occupant P sitting on a vehicle seat in the front-and-rear direction (i.e., disposed on the seat center line L), but the present disclosure is not limited to the above exemplary embodiment. For example, as in airbag devices  44  and  46  relating to a fourth exemplary embodiment and a fifth exemplary embodiment, which are illustrated in  FIG. 12 , the airbag  16  may be structured to include a main chamber portion  48  corresponding to the center chamber portion  18  (see  FIG. 11  and so forth), which serves as the first chamber portion, and the one of the right side chamber portion  22  and the left side chamber portion  20  that is disposed at the vehicle width direction inner side relative to the main chamber portion  48 . In this structure, the head H of a vehicle occupant P may be restrained by the head H of the vehicle occupant P moving into the right side slit  26  or left side slit  24  of the airbag  16 . In a case in which a curtain airbag  50  is provided that expands into a curtain shape, toward the vehicle lower side from a vehicle width direction outer side end portion of a roof headlining, the curtain airbag  50  is expanded at the vehicle width direction outer side of the main chamber portion  48 . Therefore, the head H of the vehicle occupant P may be restrained by the head H of the vehicle occupant P moving to between the main chamber portion  48  and the side curtain airbag  50 . 
         [0079]    As illustrated in  FIG. 13 , the airbag  16  that structures a portion of the airbag device  44  for a driver seat or the airbag device  46  for an assistant driver seat is fabricated employing a first sheet member  52  and a second sheet member  54  that are sheet-shaped and are formed in predetermined shapes. The first sheet member  52  is provided with a front side first extension portion  52 A and a front side second extension portion  52 B, which are to structure a region over the vehicle width direction outer side from the vehicle front side of the airbag  16  in the completed expansion state and a region over the vehicle width direction inner side from the vehicle front side, respectively. A gas generation device insertion hole  52 C is formed at a boundary between the front side first extension portion  52 A and the front side second extension portion  52 B. The gas jetting-out portion of the gas generation device  14  (see  FIG. 1 ), which is the portion at which the gas is jetted out, is to be inserted into the gas generation device insertion hole  52 C. The second sheet member  54  is provided with a rear side first extension portion  54 A and a rear side second extension portion  54 B, which are to structure a region at the vehicle width direction outer side and a region at the vehicle width direction inner side of a region at the vehicle rear side of the airbag  16  in the completed expansion state. First, the main chamber portion  48  is formed by an outer periphery portion of the front side first extension portion  52 A of the first sheet member  52  being joined to an outer periphery portion of the rear side first extension portion  54 A of the second sheet member  54  (a first step). Then, the left side chamber portion  20  or right side chamber portion  22  is formed by an outer periphery portion of the front side second extension portion  52 B of the first sheet member  52  being joined to an outer periphery portion of the rear side second extension portion  54 B of the second sheet member  54  (a second step). Then, an end portion at one side of the tether  34  (see  FIG. 12 ) and an end portion at another side of the tether  34  are joined to, respectively, an upper end portion of the main chamber portion  48  and an upper end portion of the left side chamber portion  20  or right side chamber portion  22  (a third step). Thus, the airbag  16  that structures a portion of the airbag device  44  or  46  is fabricated. The order of the first to third steps described above may be modified. 
         [0080]    Hereabove, exemplary embodiments of the present disclosure have been described. The present disclosure is not limited by these descriptions, and it will be clear that numerous modifications outside of these descriptions may be embodied within a technical scope not departing from the spirit of the disclosure.