Patent Publication Number: US-10315607-B2

Title: Vehicle occupant protection device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/286,172, filed Oct. 5, 2016, and is based on and claims priority under 35 U.S.C. § 119 from Japanese Patent Application No. 2015-237979, filed on Dec. 4, 2015. The entire contents of each of the above applications are incorporated by reference herein in entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to a vehicle occupant protection device. 
     Related Art 
     An airbag device is known (see Japanese Patent Application Laid-Open (JP-A) No. 2000-344044) that, in the event of a collision, supplies gas from an inflator through a gas supply pipe that is fixed to a seat back to a bag that is attached to the gas supply pipe, and causes this bag to inflate so as to cover a front and sides of a head portion of a vehicle occupant. In addition, an airbag device is known (see JP-A No. 2013-018378) in which an airbag for a head portion is deployed towards the front at left and right end portions of a seat headrest, and these join together at the front surface of the vehicle occupant head portion, while an auxiliary airbag for a head portion is deployed towards the front from a central portion of the seat headrest so as to join with the pair of head portion airbags. In addition to these, a structure in which an airbag that inflates so as to cover the front and sides of the head portion of a vehicle occupant is housed in a seat back is disclosed in German Patent Application Publication No. 19859988A1. 
     In the structure disclosed in JP-A No. 2000-344044, because the gas supply pipe is provided such that it protrudes above the seat back, it has an unattractive appearance and the gas supply pipe is an obstruction when the vehicle seat is being operated. 
     On the other hand, in the structure disclosed in JP-A No. 2013-018378, it is difficult to guarantee a satisfactory mutual join strength between the pair of head portion airbags that are joined together after being inflated and deployed, or a satisfactory join strength when the auxiliary head portion airbag is joined to the pair of head portion airbags. 
     As a measure to counter such drawbacks, consideration may be given to employing a structure in which an airbag that is formed as an integrated bag body is housed in a rearward side of a headrest main body, and this airbag is inflated and deployed so as to cover the head portion of a vehicle occupant from the front and from both the left and right sides. However, because the headrest main body is disposed in front of the airbag, there is a possibility that it will be difficult to make the airbag inflate and deploy on the seat front side, and the airbag will be badly obstructed by the head portion of the vehicle occupant or the vehicle cabin ceiling or the like when it passes over the headrest main body and the head portion of the vehicle occupant. Because of this, there is room for improvement from the standpoint of improving the deployment performance of the airbag. 
     SUMMARY 
     In consideration of the above-described circumstances, it is an object of the present invention to provide a vehicle occupant protection device that, in a structure in which an airbag which is constructed as an integrated bag body is housed in a folded state in rearward side of a headrest main body, makes it possible to improve the deployment performance of the airbag. 
     A vehicle occupant protection device according to a first aspect of the present invention includes an airbag that is inflated and deployed upon being supplied with gas, and that is constructed as an integrated bag body that is deployed in an area that includes a front side of a head portion of a vehicle occupant, and in an area that incudes both left and right sides of the head portion of the vehicle occupant so as to cover the head portion, and also includes an airbag case that is constructed so as to include a box-shaped case main body that is provided on a seat rear side of a headrest main body which supports the head portion from the rear, and in which the airbag is housed in a folded state, and that is formed from resin, and whose upper portion opens up during an inflation and deployment of the airbag, and so as to include a reaction force plate that is provided in a lower portion side of the case main body, and is formed by a component having greater rigidity than the case main body, and that supports the airbag from the seat rear side during the inflation and deployment of the airbag. 
     In the vehicle occupant protection device according to the first aspect of the present invention, an airbag case is provided on the seat rear side of the headrest main body, and an airbag is housed in a folded state inside this airbag case. Here, the airbag is constructed as an integrated bag body that is deployed in an area that includes a front side of a head portion of a vehicle occupant, and in an area that incudes both left and right sides of the head portion of the vehicle occupant so as to cover the head portion, and inflates and deploys upon being supplied with gas. As a consequence, the head portion of the vehicle occupant is restrained and protected by the airbag in various different types of collision. 
     Moreover, the airbag case is provided with a box-shaped case main body that is formed from resin, and this case main body is formed such that an upper portion thereof is opened up when the airbag is inflated and deployed. In addition, a reaction plate that is formed by a component having greater rigidity than the case main body is provided in the lower portion side of the case main body, and the airbag is supported from the seat rear side by this reaction force plate when the airbag is being inflated and deployed. As a consequence, reaction force towards the seat front side is applied from the reaction force plate to the airbag, and it becomes easy to make the airbag inflate and deploy towards the seat front side from the upper portion of the case main body. 
     A vehicle occupant protection device according to a second aspect of the present invention is characterized in that, in the structure according to the first aspect, the reaction force plate is provided with a rear wall reinforcement portion that is disposed in parallel with a rear wall of the case main body, and side wall reinforcement portions that extend towards the seat front side in parallel with side walls of the case main body from both sides in the seat transverse direction of the rear wall reinforcement portion, and seat front sides of the side wall reinforcement portions either slope or are curved such that, when viewed from the seat transverse direction, a lower portion of each side wall reinforcement portion is located closer to the seat front side than an upper portion of each side wall reinforcement portion. 
     In the vehicle occupant protection device according to the second aspect of the present invention, during the inflation and deployment of the airbag, reaction force towards the seat front side is applied to the airbag from the rear wall reinforcement portion that is disposed in parallel with a rear wall of the case main body. Here, side wall reinforcement portions extend towards the seat front side in parallel with side walls of the case main body from both sides in the seat transverse direction of the rear wall reinforcement portion. As a consequence, compared with a structure in which the side wall reinforcement portions are not provided, it is possible to increase the rigidity of the reaction force plate, and to increase the reaction force that is applied to the airbag. 
     Moreover, the seat front sides of the side wall reinforcement portions of the reaction force plate either slope or are curved such that, when viewed from the seat transverse direction, a lower portion of each side wall reinforcement portion is located closer to the seat front side than an upper portion of each side wall reinforcement portion. As a consequence of this, it is possible to reduce the surface area of the side wall reinforcement portions, while securing sufficient rigidity in the lower portion of the reaction force plate, and to prevent the reaction force plate from interfering with the airbag when this is inflated and deployed in the seat transverse direction from the case main body. 
     A vehicle occupant protection device according to a third aspect of the present invention is characterized in that, in the structure according to the first or second aspects, the airbag is constructed so as to include an outward roll-fold portion that is folded into a roll shape that is rolled up from a front end side of the airbag when this is in a deployed state towards an outer surface side, and is housed in the airbag case in this state, and a bellows-fold portion that is folded into a bellows fold underneath the outward roll-fold portion, and is housed in the airbag case in this state, wherein the outward roll-fold portion is housed in a location where, when viewed from the seat transverse direction, it does not overlap with the side wall reinforcement portions. 
     In the vehicle occupant protection device according to the third aspect of the present invention, when gas is supplied to the airbag, the outward roll-fold portion is inflated and deployed towards the seat front side over the top of the headrest main body and the vehicle occupant as the outward roll-fold is unwound. Here, because the outward roll-fold portion is housed in a location where, when viewed from the seat transverse direction, it does not overlap with the side wall reinforcement portions of the reaction force plate, it is possible to prevent the inflation and deployment of the outward roll-fold portions from being obstructed by the side wall reinforcement portions. 
     As has been described above, according to the vehicle occupant protection device according to the first aspect of the present invention, the excellent effect is achieved that, in a structure in which an airbag which is constructed as an integrated bag body is housed in a folded state in a rearward side of a headrest main body, it is possible to improve the deployment performance of the airbag. 
     According to the vehicle occupant protection device according to the second aspect of the present invention, the excellent effect is achieved that it is possible to cause an airbag to inflate and deploy effectively in a seat transverse direction at the same time as the reaction force applied to the airbag is increased. 
     According to the vehicle occupant protection device according to the third aspect of the present invention, the excellent effect is achieved that it is possible to cause the outward roll-fold portion to inflate and deploy towards the seat front side in such a way that it passes rapidly over a headrest main body and the head portion of a vehicle occupant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a side view showing in typical form an operating state of a vehicle occupant protection device according to an exemplary embodiment; 
         FIG. 2  is a front view showing in typical form an operating state of a vehicle occupant protection device according to an exemplary embodiment; 
         FIG. 3A  is a view showing an inflated and deployed state of a multi-directional airbag that forms part of a vehicle occupant protection device according to a first exemplary embodiment, and is a cross-sectional view taken along a line  3 A- 3 A in  FIG. 1 ; 
         FIG. 3B  is a view showing an inflated and deployed state of a multi-directional airbag that forms part of the vehicle occupant protection device according to the first exemplary embodiment, and is a cross-sectional view taken along a line  3 B- 3 B in  FIG. 1 ; 
         FIG. 4A  is a side view showing the schematic overall structure prior to operation of a vehicle occupant protection device according to an exemplary embodiment; 
         FIG. 4B  is a front view showing the schematic overall structure prior to operation of a vehicle occupant protection device according to an exemplary embodiment; 
         FIG. 5  is an enlarged perspective view showing in typical form an enlargement of a headrest according to an exemplary embodiment; 
         FIG. 6  is an enlarged typical side view showing in a partially cutaway state an enlargement of a headrest according to an exemplary embodiment, and shows a state prior to an airbag being inflated and deployed; and 
         FIG. 7  is an enlarged typical side view showing in a partially cutaway state an enlargement of a headrest according to an exemplary embodiment, and shows a state immediately after an airbag has been inflated and deployed. 
     
    
    
     DETAILED DESCRIPTION 
     A vehicle occupant protection device  10  according to an exemplary embodiment of the present invention will now be described based on  FIG. 1  through  FIG. 7 . Note that an arrow FR and an arrow UP that are shown where appropriate in the drawings respectively indicate a forward direction of a vehicle seat  12  (i.e., a direction in which a seated person faces), and an upward direction. Hereinafter, unless specifically stated otherwise, if simple front-rear, up-down, or left-right directions are used, then these refer respectively to the front-rear directions of the seat, the up-down directions of the seat, and the left-right directions when facing towards the front in the seat front-rear direction. Note also that, in this exemplary embodiment, the front-rear direction of the vehicle seat  12  matches the front-rear direction of a vehicle, the up-down direction of the vehicle seat  12  matches the up-down direction of a vehicle, and the seat transverse direction of the vehicle seat  12  matches the vehicle transverse direction. Furthermore, an arrow IN which is shown where appropriate in the drawings shows a vehicle center side in the vehicle transverse direction of an automobile that is serving as a vehicle in which the vehicle seat  12  has been installed. 
     (Overall Schematic Structure of a Vehicle Occupant Protection Device) 
     As is shown in  FIG. 1 , the vehicle occupant protection device  10  is mounted in the vehicle seat  12 . The vehicle seat  12  is disposed in a position that is offset to either the left side or right side (to the left side in the present exemplary embodiment) relative to the center in the vehicle transverse direction of a vehicle body of an automobile (not shown in the drawings). This vehicle seat  12  is constructed so as to include a seat cushion  14 , a seat back  16  whose bottom end is coupled to a rear end of the seat cushion  14 , and a headrest  18  that is provided at an upper end of the seat back  16 . 
     Note that, in  FIG. 1  through  FIG. 4B , a state is shown in which a collision test dummy D is seated on the seat cushion  14  of the vehicle seat  12  so as to serve as a model of the vehicle occupant who is to be protected. This dummy D is, for example, a World SID (Internationally integrated side impact dummy: World Side Impact Dummy) AM50 (i.e., the 50th percentile of American adult males). This dummy D is seated in a standard sitting posture (i.e., in a normal state) that is determined using a collision test method. The vehicle seat  12  is located in a reference set position that corresponds to the aforementioned sitting posture. Note that a head portion H of the dummy D is a portion above the neck and including the face, and the face faces towards the vehicle front side (i.e., the seat front side). Hereinafter, the dummy D will be referred to as the ‘vehicle occupant D’ in order to simplify the description. 
     As is shown in  FIG. 1  and  FIG. 2 , the vehicle occupant protection device  10  is constructed so as to include a multidirectional airbag device  20  that is intended to protect the vehicle occupant D from various types of collision, a side airbag device  22 , and a seatbelt device  24 . Hereinafter, the schematic structure of the seatbelt device  24  and the side airbag device  22  will be described, and thereafter the detailed structure of the multidirectional airbag device  20  will be described. 
     The seatbelt device  24  is a three-point type of seatbelt device. One end of a belt (i.e., a webbing)  28  is wound onto a retractor  26  such that it is able to be unwound therefrom, while another end of the belt  28  is fixed to an anchor  24 A. A tongue plate  24 T is provided such that it is able to slide along the belt  28 , and the vehicle occupant D puts on the belt  28  by engaging this tongue plate  24 T with a buckle  24 B. When the belt  28  is being worn by the vehicle occupant D, it includes a shoulder belt  28 S that fits around an upper body of the vehicle occupant D, and a lap belt  28 L that extends from the tongue plate  24 T to the anchor  24 A and fits around the waist portion of the vehicle occupant D. 
     In the present exemplary embodiment, the seatbelt device  24  is formed as what is known as a ‘seatbelt device with attached seat’ in which the retractor  26 , the anchor  24 A, and the buckle  24 B are provided on the vehicle seat  12 . Moreover, in this exemplary embodiment, when operated, the retractor  26  also has a pretensioner function whereby it forcibly retracts the belt  28 . Operations of the pretensioner function of the retractor  26  are controlled by an ECU (Electronic Control Unit)  60  (described below—see  FIG. 4A ). 
     The airbag device  22  is constructed so as to include an inflator  22 A and a side airbag  22 B, and is housed in a side portion on the outer side in the vehicle transverse direction of the seat back  16  with the side airbag  22 B in a folded state. When the inflator  22 A is operated, it generates gas inside the side airbag  22 B. According to this structure, this gas causes the side airbag  22 B to protrude towards the front from the side portion of the seat back  16 , and to inflate and deploy on the outer side in the vehicle transverse direction relative to the vehicle occupant D. In this exemplary embodiment, the side airbag  22 B is constructed such that it is inflated and deployed on the outer side in the vehicle transverse direction of a pelvic portion P, an abdominal portion A, a breast portion B, and a shoulder portion S of the vehicle occupant D. Operations of the inflator  22 A are also controlled by the ECU  60  (described below—see  FIG. 4A ). 
     (Multi-directional Airbag Device Structure) 
     As is shown in  FIG. 1  through  FIG. 3B , the multi-directional airbag device  20  is constructed so as to include a multi-directional airbag  30 , which serves as an airbag, an inflator  32 , and an airbag case  50 . The multi-directional airbag device  20 , which is formed having a modular structure, is provided on the seat rearward side of the headrest  18  above the seat back  16 . 
     The multi-directional airbag  30  is constructed as a single integrated bag body that is inflated and deployed so as to cover the head portion H of the vehicle occupant D (hereinafter, this will usually be referred to simply as the ‘head portion H’) from the front and from both the left and right sides thereof. More specifically, the multi-directional airbag  30  is constructed so as to include a pair of left and right frame ducts  35  that are inflated and deployed at a distance from each other in an area that includes both the left and right sides and the top of the head portion H, a forward-deploying portion  36  that deploys in an area that includes the front of the head portion H, a pair of side-deploying portions  38  that deploy in an area that includes the both the left and right sides of the head portion H, and an upward-deploying portion  48  that deploys in an area that includes the top of the head portion H. 
     The frame ducts  35  are provided as a pair with one frame duct  35  being provided on each side in the seat transverse direction of the head portion H, and are constructed such that each frame duct  35  inflates and deploys substantially in a U-shape that is open in a downward direction when seen in a side view. Specifically, when seen in a side view, in an inflated and deployed state, the frame ducts  35  include a rear duct  35 R that extends vertically in parallel with the head rest  18 , an upper duct  35 U that extends towards the front from an upper end of the rear duct  35 R, and a front duct  35 F that hangs downwards from a front end of the upper duct  35 U. 
     The forward-deploying portion  36  is constructed so as to include a forward-inflating portion  40  that includes a portion that is deployed to the front of the head portion H, and non-inflating portions  42  that divide the forward-inflating portion  40  into a plurality of inflating portions. In this exemplary embodiment, the forward-inflating portion  40  is constructed so as to include a pair of up-down inflating portions  40 A that are inflated and deployed adjacently to each other in the seat transverse direction such that the longitudinal direction of each up-down inflating portion  40 A is aligned with the up-down direction, and a lower inflating portion  40 L that is located underneath the pair of up-down inflating portions  40 A. The pair of up-down inflating portions  40 A are constructed such that they inflate and deploy at the front (i.e., at a front surface) of the head portion H, while the lower inflating portion  40 L is constructed such that it inflates and deploys at the front of the breast portion B and the shoulder portions S of the vehicle occupant D. 
     The non-inflating portions  42  are constructed so as to include a non-inflating portion  42 A that divides the pair of up-down inflating portions  40 A in the seat transverse direction, and non-inflating portions  42 B that are interposed between the respective up-down inflating portions  40 A and the front ducts  35 F of the frame duct  35 . In this exemplary embodiment, the non-inflating portion  42 A is formed by a linear seam that extends up and down, while the non-inflating portions  42 B are each formed as a portion that is surrounded by a toroidal (i.e., endless) seam that extends up and down. 
     The side-deploying portions  38  are constructed so as to include side-inflating portions  44  that, upon being supplied with gas, are inflated and deployed at the sides of the head portion H, and non-inflating portions  46  that divide the side-inflating portions  44  into a plurality of inflating portions. In this exemplary embodiment, in an inflated and deployed state, the side-deploying portions  38  are surrounded on three sides, namely, the rear, the top, and the front by the frame duct  35 , so as to be formed substantially in a rectangular shape when seen in a side view. The side-deploying portions  38  have a sufficiently large size (i.e., surface area) to enable them to wrap around substantially the entire head portion H when seen in a side view. The side-inflating portions  44  of the side-deploying portions  38  are partitioned from the frame duct  35  by a U-shaped seam  46 A which is one of the seams of the non-inflating portions  46 , and which is formed in an inverted U shape that is open towards the bottom. In this exemplary embodiment, front end sides of the side-inflating portions  44  of the side-deploying portions  38  are connected indirectly to the forward-inflating portion  40  via the front ducts  35 F of the frame ducts  35 . 
     The non-inflating portions  46  are constructed so as to include a pair of front and rear vertical seams  46 B that extend from a bottom edge of the side-inflating portion  44  to an interior of an aperture in the U-shaped seam  46 A. The pair of vertical seams  46 B are constructed such that they divide a lower portion  44 L of each side-inflating portion  44  into three inflating portions  44 L 1 ,  44 L 2 , and  44 L 3  that are inflated and deployed adjacently to each other in the front-rear direction. As a result of the lower portion  44 L of the side-inflating portions  44  being divided in this manner into the three inflating portions  44 L 1  through  44 L 3 , the front-rear length in a planar cross-sectional view of the lower portion  44 L of each side-inflating portion  44  in an inflated and deployed state is made shorter than the front-rear length in a planar cross-sectional view of the upper portion  44 U of each side-inflating portion  44 . 
     In the left and right side-deploying portions  38 , when the multi-directional airbag  30  is in an inflated and deployed state, the lower ends  44 B of the respective side-inflating portions  44  are in contact with a top of the shoulder portions S of the vehicle occupant D. In this structure, the position in the up-down direction of the multi-directional airbag  30  in an inflated and deployed state relative to (the head portion H of) the vehicle occupant D is determined by this contact of the lower end  44 B of each side-deploying portion  44  with the shoulder portions S. The multi-directional airbag  30  is constructed such that, when in this positioned state, none of the forward-deploying portion  36 , the left and right side deploying portions  38 , and the upward-deploying portion  48  (described below) come into contact with the head portion H of the vehicle occupant D (i.e., such that a gap is formed between them) when the vehicle occupant D is seated in the standard sitting posture. 
     The upward-deploying portion  48  is a deployment portion that, with the seat transverse direction taken as the longitudinal direction thereof, inflates and deploys above the head portion H. A seam (not shown in the drawings), which is a non-inflating portion, is provided in the upward-deploying portion  48 , and the thickness in the seat up-down direction of the upward-deploying portion  48  is restricted by this seam. 
     The multi-directional airbag device  30  that is constructed in the above-described manner is formed, as an example, as an integrated bag body by an OPW (One Piece Woven). As is shown in  FIG. 6 , the multi-directional airbag  30  is housed in a folded state inside an airbag case  50  (described below). Specifically, when housed within the airbag case  50 , the multi-directional airbag  30  is constructed so as to include an outward roll-fold portion  30 A that is folded in an outwards roll-fold, and a bellows-fold portion  30 B that is folded in a bellows fold. The outward roll-fold portion  30 A is folded into a roll shape that is rolled up from a front end side of the multi-directional airbag  30  when this is in a deployed state towards an outer surface side of the forward-deploying portion  36 , and is folded in such a way that, during inflation and deployment, it is easily able to be deployed towards the seat front side. The bellows-fold portion  30 B is located underneath the outward roll-fold portion  30 A, and is constructed such that gas supplied from the inflator  32  flows to the outward roll-fold portion  30 A via the bellows-fold portion  30 B. Note that it is also possible, for example, to form the multi-directional airbag  30  as an integrated bag body by cutting and sewing peripheral edges of two pieces of woven cloth. 
     As is shown in  FIG. 1 , the inflator  32  is provided together with the multi-directional airbag  30  inside the airbag case  50 . A combustion-type or cold gas-type of inflator is employed as the inflator  32 , and the gas that is generated as a result of the inflator  32  being operated is supplied to the interior of the multi-directional airbag  30 . The inflator  32  of the present exemplary embodiment is a cylinder-type of inflator, and is disposed such that a longitudinal direction thereof extends in the seat transverse direction. Furthermore, as is shown in  FIG. 4A , operations of the inflator  32  are controlled by the ECU  60  serving as a control device. 
     (ECU Structure) 
     The ECU  60  is electrically connected to the retractor  26  of the seatbelt device  24 , the inflator  22 A of the side airbag device  22 , and the inflator  32  of the multi-directional airbag device  20 . Moreover, the ECU  60  is also electrically connected to a collision prediction sensor  62  such as a pre-crash sensor and to a collision sensor  64 . 
     Based on signals from the collision prediction sensor  62 , the ECU  60  is able to predict whether or not various types of collision are unavoidable for that vehicle. The collision prediction sensor  62  is constructed, for example, so as to include a stereo camera (not shown in the drawings) that is provided adjacent to the center in the vehicle transverse direction of an upper portion of the windshield glass. An area in the front of the vehicle is photographed by this stereo camera, and objects that may collide with the vehicle are detected. In addition, the distance to a collision object detected by the stereo camera, and the relative speed between the vehicle and the collision object are also measured, and this measurement data is output to the ECU  60 . Based on this measurement data from the stereo camera, the ECU  60  determines whether or not a collision with the vehicle is unavoidable. Note that a milliwave radar or the like may be used for the collision prediction sensor  62 . 
     When the ECU  60  has detected a vehicle collision based on a signal from the collision sensor  64 , it causes a pretensioner mechanism of the retractor  26  to be operated, and also causes the inflator  32  to be operated. As a consequence, gas generated by the inflator  32  is supplied to the multi-directional airbag  30 . Note that, as an example, the collision sensor  64  is constructed so as to include a front satellite sensor that is formed by an acceleration sensor that is disposed on a front side member, and a floor sensor that is formed by an acceleration sensor that is disposed on the floor underneath the center console. 
     (Structure of the Airbag Case  50 ) 
     Next, the structure of the airbag case  50  will be described. As is shown in  FIG. 5 , the airbag case  50  is provided in a seat rear side of a headrest main body  19  that forms part of the headrest  18 . The headrest main body  19  is disposed at the rear of the head portion H of the vehicle occupant D so as to be able to support the head portion H of the vehicle occupant D from the rear, and is internally provided with cushioning material. The headrest main body  19  is joined via stays  21  to the seat back  16  (see  FIG. 1 ). 
     The airbag case  50  which is provided on the seat rear side of the headrest main body  19  is constructed so as to include a case main body  52  and a reaction force plate  54 . The case main body  52  is formed from resin substantially in a box shape, and also functions as a decorative cover for a rear portion of the headrest  18 . The case main body  52  is constructed so as to include a lower wall  52 A, a rear wall  52 B, and a pair of left and right side walls  52 C. 
     The lower wall  52 A is located at the same height as a lower surface of the headrest main body  19 , or alternatively slightly on the seat lower side of the lower surface of the headrest main body  19 , and is disposed such that it faces an upper end of the seat back  16 . In addition, the lower wall  52 A is also formed slightly wider in the seat transverse direction than the headrest main body  19 , and both end portions in the seat transverse direction of the lower wall  52 A are located on the outer side in the seat transverse direction of the headrest main body  19 . 
     The rear wall  52 B extends towards the seat upper side from a rear end portion of the lower wall  52 A, and in a side view looking from the seat transverse direction, slopes gradually towards the rear as it moves from the upper side towards the lower side. Moreover, a top end of the rear wall  52 B curves towards the headrest main body  19  (see  FIG. 6 ). 
     The pair of left and right side walls  52 C extend towards the seat upper side from both end portions in the seat transverse direction of the lower wall  52 A, and this pair of side walls  52 C are disposed facing each other in the seat transverse direction. Rear edges of each of the pair of side walls  52 C are joined respectively to the rear wall  52 B, and in a side view looking from the seat transverse direction, are formed such that they slope gradually towards the rear as they move from the upper side towards the lower side. 
     As is described above, the case main body  52  is formed substantially in a box shape that is open on the seat forward side, and a space is provided between the case main body  52  and the headrest main body  19  where the multi-directional airbag  30  is housed. Moreover, as is shown in  FIG. 4B , the aperture on the seat front side of the case main body  52  is closed off by an airbag door  33 . In the present exemplary embodiment, when seen in a front view, the space between the airbag case  50  and the headrest main body  19  is closed off by the airbag door  33 , and a structure is employed in which, triggered by a tear line  33 A, the airbag door  33  is split open by inflation pressure from the multi-directional airbag  30  so that the multi-directional airbag  30  is allowed to inflate and deploy towards the front. 
     As is shown in  FIG. 5 , the case main body  52  is formed from resin as a single body, and the reaction force plate  54  is formed integrally with the case main body  52  on the lower portion side thereof. The reaction force plate  54  is formed by a component having greater rigidity than the case main body  52 , and in the present exemplary embodiment, as an example, is made from metal. The reaction force plate  54  is formed integrally with the case main body  52  by being insert-molded inside the case main body  52 . The reaction force plate  54  is constructed so as to include a lower wall reinforcement portion  54 A, side wall reinforcement portions  54 C, and a rear wall reinforcement portion  54 B. 
     The lower wall reinforcement portion  54 A is disposed inside the lower wall  52 A of the case main body  52 , and is formed slightly smaller than the lower wall  52 A. The rigidity of the lower surface of the airbag case  50  is increased by this lower wall reinforcement portion  54 A. 
     The rear wall reinforcement portion  54 B extends from a rear end of the lower wall reinforcement portion  54 A in parallel with the rear wall  52 B of the case main body  52  towards the seat upper side, and is disposed inside the rear wall  52 B. A top end portion of the rear wall reinforcement portion  54 B is located slightly on the seat upper side of an intermediate portion in the seat up-down direction of the rear wall  52 B, and the rear wall reinforcement portion  54 B does not extend as far as the upper portion of the rear wall  52 B. The rigidity of the lower portion side of the rear surface of the airbag case  50  is increased by this rear wall reinforcement portion  54 B. 
     The side wall reinforcement portions  54 C extend from both sides in the seat transverse direction of the rear wall reinforcement portion  54 B in parallel with the side walls  52 C of the case main body  52  towards the seat front side, and are disposed inside the side walls  52 C of the case main body  52 . Lower ends of the side wall reinforcement portions  54 C are joined to the lower wall reinforcement portion  54 A. Furthermore, seat front sides of the side wall reinforcement portions  54 C either slope or are curved such that, when viewed from the seat transverse direction, a lower portion thereof is located closer to the seat front side than an upper portion thereof. The seat front sides of the side wall reinforcement portions  54 C of the present exemplary embodiment are curved such that a lower portion thereof is located closer to the seat front than an upper portion thereof. Because of this, the side wall reinforcement portions  54 C are formed in a substantially triangular shape in which, when viewed from the seat transverse direction, a corner portion on the front portion side and the top portion side of the rectangle is cut away towards the inner side. Moreover, as is shown in  FIG. 6 , the side wall reinforcement portions  54 C are formed in a shape in which, when viewed from the seat transverse direction, they avoid the outward roll-fold portion  30 A of the multi-directional airbag  30 . In other words, the outward roll-fold portion  30 A is housed in a position where it does not overlap with the side wall reinforcement portions  54 C when viewed from the seat transverse direction. 
     The rigidity of the lower portion side of the case main body  52  is increased by the reaction force plate  54  which is constructed in the manner described above. Moreover, as is shown in  FIG. 7 , during the inflation and deployment of the multi-directional airbag  30 , the upper portion of the airbag case  50  where the reaction force plate  54  is not provided is opened up by inflation pressure, and is deformed towards the seat rear side. As a consequence, a structure is created in which the multi-directional airbag  30  is deployed towards the seat front side. 
     (Operation and Effects) 
     Next, an operation of the exemplary embodiment will be described. 
     In the vehicle occupant protection device  10  of the present exemplary embodiment, the metal reaction force plate  54  is provided on the lower portion side of the case main body  52  of the airbag case  50 , and the rigidity of the lower portion side of the case main body  52  is increased by this reaction force plate  54 . As a consequence, when the upper portion of the airbag case  50  is opened by the inflation pressure of the multi-directional airbag  30 , it is possible to prevent the lower portion side of the case main body  52  from deforming towards the seat rear side. In addition, because the multi-directional airbag  30  is supported from the seat rear side by the rear wall reinforcement portion  54 B of this reaction force plate  54 , reaction force towards the seat front side is applied to the multi-directional airbag  30  from the rear wall reinforcement portion  54 B. As a result, it is easy to make the multi-directional airbag  30  inflate and deploy towards the seat front side from the upper portion of the case main body  52 . Namely, the deployment performance of the multi-directional airbag  30  can be improved. 
     Moreover, in the present exemplary embodiment, as is shown in  FIG. 5 , the side wall reinforcement portions  54 C extend towards the seat front side in parallel with the side walls  52 C of the case main body  52  from both sides in the seat transverse direction of the rear wall reinforcement portion  54 B of the reaction force plate  54 . As a consequence of this, it is possible to increase the flexural rigidity towards the seat rear side of the rear wall reinforcement portion  54  of the reaction force plate  54 , and it is possible to prevent the lower portion of the rear surface of the airbag case  50  from deforming towards the rear side during the inflation and deployment of the multi-directional airbag  30 . Moreover, the side wall reinforcement portions  54 C either slope or are curved such that, when viewed from the seat transverse direction, a lower portion thereof is located closer to the seat front side than an upper portion thereof. As a consequence, compared with a structure in which the side wall reinforcement portions  54 C are formed in a rectangular shape when viewed from the seat transverse direction, it is possible to reduce the surface area of the side wall reinforcement portions  54 C, and to prevent the reaction force plate  54  from interfering with the multi-directional airbag  30  when this is inflated and deployed in the seat transverse direction from the case main body  52 . In this manner, it is possible to prevent the inflation and deployment of the multi-directional airbag  30  being obstructed in the seat transverse direction and, at the same time, to increase reaction force applied to the multi-directional airbag  30 . 
     Furthermore, in the present exemplary embodiment, because the outward roll-fold portion  30 A is housed in a position where it does not overlap with the side wall reinforcement portions  54 C of the reaction force plate  54  when viewed from the seat transverse direction, it is possible to prevent the inflation and deployment of at least the outward roll-fold portion  30 A from being obstructed by the side wall reinforcement portions  54 C. Moreover, the bellows-fold portion  30 B is provided underneath the outward roll-fold portion  30 A, and gas generated from the inflator  32  is supplied to the outward roll-fold portion  30 A via the bellows-fold portion  30 B. As a consequence, because the bellow-fold portion  30 B is inflated and deployed before the outward roll-fold portion  30 A, the outward roll-fold portion  30 A is pushed upwards, and the outward roll-fold portion  30 A can be rapidly inflated and deployed towards the seat front side of the headrest main body  19 . 
     Furthermore, in the present exemplary embodiment, the multi-directional airbag  30  is constructed as an integrated bag body that is deployed in an area that includes the front side of the head portion H of the vehicle occupant D, and in an area that incudes both the left and right sides thereof so as to cover the head portion H of the vehicle occupant D. As a consequence, in the event of a vehicle collision, because the head portion H of the vehicle occupant D is covered by the multi-directional airbag  30 , it is possible to restrain and protect the head portion H of the vehicle occupant D in various different types of collision. 
     Moreover, in the present exemplary embodiment, the multi-directional airbag  30  is housed in the airbag case  50  which is provided on the seat rear side of the headrest main body  19 . Because of this, compared with a structure in which, for example, a gas supply pipe that is disposed so as to surround the head portion H of the vehicle occupant D from above protrudes at all times into the vehicle cabin interior, it is possible to improve the pre-operating appearance, while guaranteeing a level of vehicle occupant protection equal to or surpassing that provided by the above structure. Moreover, adjustment of the front-rear position, adjustment of the height, and reclining operations and the like of the vehicle seat  12  are not obstructed by the multi-directional airbag device  20 . 
     The vehicle occupant protection device  10  according to an exemplary embodiment of the present invention has been described above, however, it is to be understood that the present invention may be implemented in a variety of forms insofar as they do not depart from the spirit or scope of the present invention. For example, as is shown in  FIG. 5 , the reaction force plate  54  of the present exemplary embodiment is constructed so as to include the lower wall reinforcement portion  54 A, the rear wall reinforcement portion  54 B, and the side wall reinforcement portions  54 C, however, the present invention is not limited to this. It is also possible for the reaction force plate  54  to be formed by only the lower wall reinforcement portion  54 A and the rear wall reinforcement portion  54 B. In this case, the side walls  52 C of the case main body  52  may also be formed by resin components having a high degree of rigidity. Moreover, the reaction force plate  54  may also be formed by only the rear wall reinforcement portion  54 B and the side wall reinforcement portions  54 C. 
     Moreover, in the present exemplary embodiment, the seat front side of each side wall reinforcement portion  54 C is curved such that a lower portion thereof is located closer to the seat front than an upper portion thereof when viewed from the seat transverse direction, however, the present invention is not limited to this. For example, it is also possible to employ a structure in which the seat front side of each side wall reinforcement portion  54 C slopes such that, when viewed from the seat transverse direction, a lower portion thereof is located closer to the seat front than an upper portion thereof. In this case as well, compared with a structure in which, when viewed from the seat transverse direction, rectangular-shaped side wall reinforcement portions are provided, it is possible to prevent the multi-directional airbag  30  being obstructed by the side wall reinforcement portions  54 C during inflation and deployment. 
     Furthermore, from the standpoint of hastening the inflation and deployment of the multi-directional airbag  30 , it is also possible to employ a structure in which, when the outward roll-fold portion  30 A is housed, it is positioned on the front side of the inside of the airbag case  50  so that, when viewed from the seat transverse direction, the outward roll-fold portion  30 A and the side wall portions  54 C do not overlap with each other. For example, if a positioning component such as a urethane pad or the like is disposed in a rear portion of the inside of the airbag case  50 , then the outward roll-fold portion  30 A can be positioned on the front side of the inside of the airbag case  50 . As a consequence, it is possible to prevent the outward roll-fold portion  30 A from moving to the rearward side of the inside of the airbag case  50  because of vibrations or the like while the vehicle is traveling, and the outward roll-fold portion  30 A can be effectively prevented from overlapping with the side wall reinforcement portions  54 C when viewed from the seat transverse direction. 
     Moreover, in the present exemplary embodiment, the reaction force plate  54  and the case main body  52  are formed as a single integral body via insert molding, however, the present invented is not limited to this. For example, it is also possible to firstly form the case main body  52  using a resin mold, and to thereafter assemble the reaction force plate  54  together with the case main body  52 . Furthermore, the reaction force plate  54  is formed from metal, however, the present invention is not limited to this, and provided that the reaction force plate  54  has greater rigidity than the case main body  52 , then the reaction force plate  54  may be formed from another material. For example, it is also possible to form the reaction force plate  54  from fiber-reinforced resin that has been reinforced with glass fibers or the like, or from reinforced resin that has been reinforced with talc (i.e., with finely ground talcum powder). In this case as well, because the rigidity of the lower portion side of the case main body  52  is increased by the reaction force plate  54 , this structure has the effect of causing a reaction force towards the seat front side to act on the multi-directional airbag  30  during inflation and deployment. 
     Furthermore, in the present exemplary embodiment, a design surface is formed on the rear portion of the headrest  18  by the airbag case  50 , however, the present invention is not limited to this. For example, it is also possible to create a sense of harmony by covering the airbag case  50  and the headrest main body  19  with upholstery. 
     Moreover, in the present exemplary embodiment, the headrest  18  and the seat back  16  are joined together by the stays  21 , however, the present invention is not limited to this. It is also possible for the headrest  18  and the seat back  16  to be formed as an integrated structure. In this case, the portion thereof that is constructed such that it is able to support the head portion H of the vehicle occupant D from the rear corresponds to the ‘headrest main body’ of the present invention. 
     Moreover, in the above-described exemplary embodiment, the inflator  32  is disposed inside the airbag case  50 , however, the present invention is not limited to this. For example, it is also possible to dispose the inflator  32  inside the upper portion of the seat back  16 . Moreover, the number and placement of the inflators  32  are not limited and it is possible, for example to dispose inflators  32  vertically inside the seat back  16  such that the longitudinal direction thereof is aligned with the seat up-down direction. 
     Furthermore, the present invention is not limited to a structure in which the seatbelt device  24  is provided in the vehicle seat  12 , and it is also possible to employ a structure in which the retractor  26 , anchor  24 A, buckle  24 B and the like are provided on the vehicle body. Moreover, in a structure in which the vehicle occupant protection device  10  is provided with the seatbelt device  24 , then the seatbelt device  24  is not limited to being a three-point type of device, and may also be a four-point type of seatbelt device or the like. 
     Moreover, in the present exemplary embodiment, an example is described in which the vehicle seat  12  is disposed such that the seat transverse direction matches the vehicle transverse direction, however, the present invention is not limited to this. For example, the vehicle seat  12  may also be disposed diagonally relative to the vehicle body, or may be constructed such that the orientation thereof relative to the vehicle body is able to be altered (by being rotated around a vertical axis). Because the multi-directional airbag  30  is inflated and deployed such that it covers the head portion H of the vehicle occupant D even if this type of structure is employed, this can also contribute to the superior protection of the head portion H. Moreover, because the multi-directional airbag  30  is housed in the headrest  18 , it is difficult for there to be any interference between the multi-directional airbag  30  and the vehicle cabin interior surfaces or vehicle cabin interior components, and any impediment to the operation to alter the orientation of the vehicle seat  12  relative to the vehicle body can be suppressed or prevented.