Patent Publication Number: US-2023158991-A1

Title: Airbag device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2021-190139 filed on Nov. 24, 2021, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The disclosure relates to an airbag device including an airbag configured to be deployed outside a vehicle upon a side collision of the vehicle. 
     In a vehicle such as an automobile, use of an airbag device including an airbag to be deployed outside the vehicle has been proposed to reduce damage to a vehicle body and an occupant upon a collision. 
     As techniques related to measures against a side collision of a vehicle, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2005-349920 discloses an occupant protection device including: an internal airbag to be deployed into a curtain shape along a side window inside a vehicle upon detection of collision from a side of the vehicle; and an external airbag to be deployed along the side window outside the vehicle upon detection of collision from the side of the vehicle. JP-A No. 2005-349920 discloses that the internal airbag and the external airbag are deployed to finally overlap with the side of the vehicle. 
     Japanese Unexamined Patent Application Publication (Translation of PCT Application) (JP-T) No. 2005-537165 discloses an occupant protection system including an external airbag system and a predictive collision detection system. In the occupant protection system, to protect an occupant in response to collision, an airbag including air chambers arranged in a front-rear direction is deployed to the vehicle-widthwise outside from the inside of a door near the occupant&#39;s seated position. 
     JP-T No. 2008-526593 discloses that, as airbags that sequentially operate to alleviate damage to a vehicle upon collision, airbags including inflation units are arranged in a horizontal direction on, for example, a side surface of a vehicle body. 
     SUMMARY 
     An aspect of the disclosure provides an airbag device to be applied to a vehicle. The vehicle is provided with a door and a side sill. The door is provided to be openable and closable at a door opening provided on a side surface of a vehicle body of the vehicle. The side sill is disposed along a lower edge of the door. The airbag device includes an airbag and an application state detector. The airbag is configured to be deployed from a container to be disposed on a lower side of the door on the vehicle body to a region on a vehicle-widthwise outside of the door. The application state detector is configured to detect a load application state of a load from the airbag to the vehicle body. The airbag includes a first air chamber, a second air chamber, and an internal pressure controller. The first air chamber is configured to transmit a load applied from the vehicle-widthwise outside to a side surface of the side sill. The second air chamber is configured to couple a lower part of the first air chamber and the container. The internal pressure controller is configured to control an internal pressure of the second air chamber based on the load application state detected by the application state detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the specification, serve to explain the principles of the disclosure. 
         FIG.  1    is a side view of a vehicle including an airbag device according to one example embodiment of the disclosure. 
         FIG.  2    is a cross-sectional view taken in a direction of arrows II-II illustrated in  FIG.  1   . 
         FIG.  3    is a diagram illustrating a configuration of a control system for an airbag in the airbag device according to one example embodiment. 
         FIG.  4    is a flowchart illustrating an overview of airbag deployment control in the airbag device according to one example embodiment. 
         FIG.  5    is a cross-sectional view of a state after a side collision in the vehicle including the airbag device according to one example embodiment. 
         FIG.  6    is a cross-sectional view of surroundings of a front side door in a vehicle including an airbag device according to one example embodiment of the disclosure. 
         FIG.  7    is a cross-sectional view of surroundings of a front side door in a vehicle including an airbag device according to one example embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In a side collision in which an object, such as another vehicle, collides from a side of a vehicle, a crash stroke in which energy is absorbable by crush of a vehicle body structure is shorter than in a front collision, which can result in an insufficient amount of energy absorption. 
     Moreover, in a side collision, a deformation speed of a door during the collision can be faster than a movement speed of a vehicle body, which can cause secondary collision damage to an occupant. 
     In view of such circumstances, providing a vehicle outside airbag device to be deployed outside a vehicle on a side surface of a vehicle body has been proposed, as in the existing techniques described above. However, in a case where a load from an object that comes into collision is applied to a door via an airbag, it is eventually difficult to sufficiently suppress deformation of the door. What is desired is to more effectively suppress entry of the door into a vehicle compartment. 
     It is desirable to provide an airbag device that suppresses collision damage upon a side collision. 
     In the following, some example embodiments of the disclosure are described in detail with reference to the accompanying drawings. Note that the following description is directed to illustrative examples of the disclosure and not to be construed as limiting to the disclosure. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting to the disclosure. Further, elements in the following example embodiments which are not recited in a most-generic independent claim of the disclosure are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Throughout the present specification and the drawings, elements having substantially the same function and configuration are denoted with the same reference numerals to avoid any redundant description. In addition, elements that are not directly related to any embodiment of the disclosure are unillustrated in the drawings. 
     First Example Embodiment 
     A description is given below of an airbag device according to a first example embodiment of the disclosure. 
     The airbag device according to the first example embodiment may be related to a vehicle, for example, an automobile such as a passenger car, provided with an occupant entry and exit door on a side surface of a vehicle compartment that accommodates an occupant. 
       FIG.  1    is a side view of the vehicle including the airbag device according to the first example embodiment. 
       FIG.  2    is a cross-sectional view taken in a direction of arrows II-II illustrated in  FIG.  1   , In the first example embodiment, a vehicle  1  may be, for example, an automobile such as a passenger car with a so-called two-box vehicle shape that includes a power unit compartment  20  protruding to a front side of a vehicle compartment  10 . 
     The vehicle compartment  10  may have a space that accommodates, for example, an occupant. The vehicle compartment  10  may include, for example, two rows of seats, i.e., front seats and rear seats, arranged in a front-rear direction. 
     A side surface of the vehicle compartment  10  may be provided with, for example, a front side door  30 , a rear side door  40 , a side sill  50 , an A pillar  60 , a B pillar  70 , a C pillar  80 , and a door beam  90 . 
     The front side door  30  may be a door-shaped body that is used for a front-seat occupant to get in or get out of the vehicle. The front side door  30  may be provided to be openable and closable at a door opening provided on a side of a front seat S in a front part of the vehicle compartment  10 . 
     The front side door  30  may have a front end swingably attached to a rear part of the A pillar  60  via an unillustrated hinge. 
     The front side door  30  may have a rear end detachably attached to a front part of the B pillar  70  via an unillustrated door catch mechanism. 
     As illustrated in  FIG.  2   , the front side door  30  may include, for example, an outer panel  31 , an inner panel  32 , and a door trim  33 . 
     The outer panel  31  and the inner panel  32  may each be, for example, a steel plate press-worked into a panel-shaped member. 
     The outer panel  31  may be a member included in an outer surface, or a design surface, of the vehicle  1 . 
     The inner panel  32  may be disposed on the vehicle-widthwise inside of the outer panel  31 . The outer panel  31  and the inner panel  32  may be joined to each other at outer peripheral edges. In a middle part of the front side door  30 , the outer panel  31  and the inner panel  32  may be opposed to each other with a space provided therebetween in a vehicle widthwise direction. 
     The inner panel  32  may be a frame-shaped member including a steel plate with a larger thickness than the outer panel  31  and having higher strength and bending stiffness than the outer panel  31 . 
     The door trim  33  may be an interior member exposed to the inside of the vehicle compartment  10 . 
     The door trim  33  may be attached to a surface of the inner panel  32  on the vehicle-widthwise inside. 
     The door trim  33  may include, for example, a resin-based material such as polypropylene (PP). 
     The rear side door  40  may be a door-shaped body that is used for a rear-seat occupant to get in or get out of the vehicle. The rear side door  40  may be provided to be openable and closable at a door opening provided on a side of an unillustrated rear seat in a rear part of the vehicle compartment  10 . 
     A front edge of the rear side door  40  may be disposed adjacent to a rear edge of the front side door  30  via an inevitably provided space or gap, in a state in which the doors are closed. 
     The rear side door  40  may have a front end swingably attached to a rear part of the B pillar  70  via an unillustrated hinge. 
     The rear side door  40  may have a rear end detachably attached to a front part of the C pillar  80  via an unillustrated door catch mechanism. 
     The side sill  50  may be a vehicle body structural member extending in the front-rear direction of the vehicle, i.e., a vehicle front-rear direction, along lower edges of the front side door  30  and the rear side door  40 . 
     The side sill  50  may be disposed along both ends of an unillustrated floor panel included in a floor surface of the vehicle compartment  10 . 
     The side sill  50  may have a front end disposed adjacent to a rear part of a front wheel house containing a front wheel FW. 
     The side sill  50  may have a rear end disposed adjacent to a front part of a rear wheel house containing a rear wheel RW. 
     A lower part of the side sill  50  may be provided with a retainer  51  serving as a container that contains an airbag  100  in an undeployed state and an inflator  211 . 
     The A pillar  60  may be a vehicle body structural member, i.e., a front pillar, provided to protrude upward from the vicinity of the front end of the side sill  50 . 
     A lower part of the A pillar  60  may be disposed along the front end of the front side door  30 . 
     The lower part of the A pillar  60  may be provided with the unillustrated hinge supporting the front side door  30  swingably about an axis extending along a vertical direction. 
     An upper part of the A pillar  60  may be exposed to be included in the outer surface of a vehicle body of the vehicle, and may be inclined rearward along a side edge of a windshield. 
     The B pillar  70  may be a vehicle body structural member, i.e., a center pillar, provided to protrude upward from an intermediate part of the side sill  50  in the front-rear direction. 
     The rear edge of the front side door  30  may be disposed along a front part of the B pillar  70 . 
     The rear end of the front side door  30  may be detachably attached to the B pillar  70  via the unillustrated door catch mechanism. 
     The front edge of the rear side door  40  may be disposed along a rear part of the B pillar  70 . 
     The rear part of the B pillar  70  may be provided with the unillustrated hinge supporting the rear side door  40  swingably about an axis extending along the vertical direction. 
     The C pillar  80  may be a vehicle body structural member, i.e., a rear pillar, provided to protrude upward from the vicinity of the rear end of the side sill  50 . 
     A rear edge of the rear side door  40  may be disposed along a front part of the C pillar  80 . 
     The rear end of the rear side door  40  may be detachably attached to the C pillar  80  via the unillustrated door catch mechanism. 
     The side sill  50 , the A pillar  60 , the B pillar  70 , and the C pillar  80  may be, for example, steel plates press-formed into panels and assembled and joined by spot welding, laser welding, a structural adhesive, etc. to each have a closed section as a cross-section extending along a plane orthogonal to a longitudinal direction. 
     The door beam  90  may be a member provided inside the front side door  30  and disposed across a front part and a rear part of the front side door  30 . 
     The door beam  90  may include, for example, a circular pipe including a steel material. 
     A front end  91  and a rear end  92  of the door beam  90  may be attached to the inner panel  32  in the vicinity of the front end and the rear end of the front side door  30 . 
     The door beam  90  may be inclined with respect to a horizontal direction in such a manner that the front end  91  is positioned higher than the rear end  92 . 
     The vehicle  1  may include the airbag  100  configured to be deployed to a region on the vehicle-widthwise outside of the front side door  30  and the rear side door  40 , in response to a symptom of a side collision (pre-crash determination). 
     The airbag  100  may be, for example, base fabric panels including nylon fibers joined to each other into a bag-shaped body by a method such as stitching or fusion. 
     The airbag  100  may be deployed by receiving a deployment gas introduced from the inflator  211  to be described later. 
     In normal use of the vehicle, including before pre-crash determination establishment and before airbag deployment, the airbag  100  may be contained in a folded state in the retainer  51  provided in the lower part of the side sill  50 . 
     The retainer  51  may serve as a part where the airbag  100  is attached on a vehicle body side after the airbag  100  is deployed. 
     As illustrated in  FIG.  2    etc., the airbag  100  may include a first air chamber  110 , a second air chamber  120 , and a third air chamber  130 . 
     The first air chamber  110  may be deployed on the vehicle-widthwise outside of the outer panel  31  and the side sill  50 . 
     The first air chamber  110  may be configured to mainly transmit a load received from an object that comes into side collision to the side sill  50  and the front side door  30 . 
     As illustrated in  FIG.  2   , a vertical distance L1 from a point P1 where the airbag  100  (the second air chamber  120 ) and the side sill  50  are fixed to each other to a point P2 where a side surface of the side sill  50  protrudes furthest to the vehicle-widthwise outside may be set equal to a vertical distance L2 from the point P2 to an upper end P3 of the first air chamber  110 . 
     The second air chamber  120  is a part provided across a lower part of the first air chamber  110  and the retainer  51  of the side sill  50  and included in a lower part of the airbag  100 . 
     The second air chamber  120  may serve as a base where the airbag  100  is attached to the vehicle body. 
     The second air chamber  120  may be configured to couple the first air chamber  110  and the side sill  50 , and control a behavior of the first air chamber  110 . 
     The control of the behavior of the first air chamber  110  by the second air chamber  120  will be described in detail later. 
     The third air chamber  130  may be a part configured to be deployed to protrude further to the upper side from an upper part of the first air chamber  110 . 
     The third air chamber  130  may be provided with an unillustrated vent hole (vent channel). 
     The third air chamber  130  may be configured to, upon receiving a load applied by collision with an object (e.g., another vehicle), contract while exhausting the deployment gas to the outside from the vent hole to absorb energy caused by the collision. 
     As illustrated in  FIG.  1   , in the side view of the vehicle, an upper end of the third air chamber  130  may be disposed to be positioned above an upper end of the door beam  90 , in a region from a front end to a rear end of a seating surface of the seat S in the vehicle front-rear direction. Note that such a positional relationship may hold, for example, in the entire region of a front-rear sliding range of the seat S. 
     The third air chamber  130  may serve as an energy absorption (EA) airbag that generates a uniform load on a contact surface with the outer panel  31  of the front side door  30 , in response to load application. 
     As illustrated in  FIG.  1   , a front end of the airbag  100  may be positioned to protrude to a vehicle front side further than the front end of the front side door  30 . 
     A rear end of the airbag  100  may be positioned to protrude to a vehicle rear side further than the rear end of the rear side door  40 . 
       FIG.  3    is a diagram illustrating a configuration of a control system for the airbag in the airbag device according to the first example embodiment. 
     A control system  200  may include, for example, an airbag control unit  210  and an environment recognition unit  220 . 
     The airbag control unit  210  and the environment recognition unit  220  may each include a microcomputer including, for example, a data processor, a storage, an input/output interface, and a bus. The data processor may be a central processing unit (CPU). The storage may be a random-access memory (RAM) or a read-only memory (ROM). The bus may couple the data processor, the storage, and the input/output interface together. 
     The airbag control unit  210  and the environment recognition unit  220  may be communicably coupled to each other, for example, directly or via an in-vehicle local area network (LAN) such as a controller area network (CAN) communication system. 
     The airbag control unit  210  may control a deployment state of the airbag  100 . 
     The airbag control unit  210  may be coupled to, for example, the inflator  211 , a pressure regulating valve  212 , an internal pressure sensor  213 , a door internal pressure sensor  214 , and a tensile load sensor  215 . 
     The inflator  211  may be a gas generator that deploys the airbag  100  by supplying the deployment gas to each of the first air chamber  110 , the second air chamber  120 , and the third air chamber  130  of the airbag  100 . 
     The inflator  211  may be configured to generate the deployment gas, for example, by causing a chemical to react in response to a deployment signal. 
     The inflator  211  may have a configuration including multiple gas generators that supply the deployment gas independently to the first air chamber  110 , the second air chamber  120 , and the third air chamber  130  of the airbag  100 . 
     In another example, the inflator  211  may be a multistage inflator that is able to generate the deployment gas multiple times at time intervals, on an as-needed basis. 
     The pressure regulating valve  212  may be provided in the second air chamber  120 , and may open and close an unillustrated vent channel that allows communication between the inside and the outside. 
     The pressure regulating valve  212  may be configured to, in response to a valve-opening command from the airbag control unit  210 , open the vent channel and release the deployment gas inside the second air chamber  120  to the outside to reduce an internal pressure of the second air chamber  120 . 
     The pressure regulating valve  212  may cooperate with the airbag control unit  210  to serve as an “internal pressure controller” in one embodiment. 
     The pressure regulating valve  212  may be in a closed state in a period from start of deployment of the airbag  100  until before collision. 
     The internal pressure sensor  213  may be a pressure sensor that detects the pressure (i.e., internal pressure) of the deployment gas inside the second air chamber  120 . 
     The door internal pressure sensor  214  may detect an air pressure in the space between the outer panel  31  and the inner panel  32  of the front side door  30 , i.e., a pressure inside the door. 
     The door internal pressure sensor  214  may serve as an application state detector that detects a load application state from the airbag  100  to the vehicle body, by detecting a change in air pressure caused by crush of the front side door  30  upon a side collision. 
     The pressure inside the door may increase with an increase in an amount of deformation of the front side door  30 , Accordingly, the door internal pressure sensor  214  may be used as a deformation amount detector that detects the amount of deformation of the front side door  30 . 
     The tensile load sensor  215  may detect a tensile load that acts between the second air chamber  120  and the retainer  51 . 
     The tensile load sensor  215  may include, for example, a load sensor such as a load cell. 
     If the first air chamber  110  collides with an object to be pushed to the vehicle-widthwise inside while deforming the front side door  30 , an upper part of the second air chamber  120  may be pulled by the lower part of the first air chamber  110 , and a tensile load may thus act on the second air chamber  120 . 
     On the basis of the tensile load, it is possible to detect the load application state from the airbag  100  to the vehicle body. 
     The tensile load sensor  215  may also serve as the application state detector and as the deformation amount detector. 
     The environment recognition unit  220  may recognize a surrounding environment including a side of the vehicle  1 , i.e., the own vehicle, on the basis of outputs of various sensors. 
     The environment recognition unit  220  may be coupled to the sensors, for example, a side-looking camera  221 , a millimeter-wave radar  222 , and a laser scanner  223 . 
     The side-looking camera  221  may include, for example, a solid-state image sensor such as a complementary metal oxide semiconductor (CMOS) or a charge-coupled device (CCD), an imaging optical system such as a lens group, and an image processor. The side-looking camera  221  may sequentially acquire images within an imaging range, i.e., an angle of view, including the side of the own vehicle. 
     The millimeter-wave radar  222  may be a radar that uses radio waves in a frequency band of, for example, 30 to 300 GHz. The millimeter-wave radar  222  may be configured to detect presence or absence of an object and a relative position of the object with respect to the vehicle  1 . 
     The laser scanner  223  may be a light detection and ranging (LiDAR). The laser scanner  223  may be configured to irradiate surroundings of the vehicle  1  with, for example, pulsed near-infrared laser light to scan the surroundings. The laser scanner  223  may thereby detect, for example, presence or absence of an object, a relative position of the object with respect to the vehicle  1 , and a shape of the object, on the basis of presence or absence of reflected light and a time difference between irradiation with the laser light and returning of reflected light. 
     For example, in a case where a side collision with an object such as another vehicle V is unavoidable, i.e., a case where pre-crash determination is established, the environment recognition unit  220  may be able to recognize a form of the collision with the object and an attribute of the object. The form of the collision with the object may be, for example, a speed vector of the object with respect to the vehicle  1  or a position where the object collides with the vehicle  1 . The attribute of the object may be, for example, a vehicle type, a vehicle shape, or a size in a case where the object is a vehicle, 
       FIG.  4    is a flowchart illustrating an overview of airbag deployment control in the airbag device according to the first example embodiment. 
     The flow is described below in order of step. 
     [Step S 01 : Pre-crash Determination Establishment] 
     The environment recognition unit  220  may determine, on the basis of the outputs of the sensors, whether collision of an object such as the other vehicle V on a side surface of the vehicle  1  is unavoidable. 
     If the environment recognition unit  220  determines that collision is unavoidable (step S 01 : Y), the environment recognition unit  220  may establish pre-crash determination, and the flow may proceed to step S 02 . Otherwise (step S 01 : N), the series of processes may be ended. 
     [Step S 02 : Airbag Deployment] 
     The environment recognition unit  220  may transmit a signal indicating that the pre-crash determination has been established to the airbag control unit  210 . 
     The airbag control unit  210  may supply the deployment signal to the inflator  211 , and the inflator  211  may start to generate the deployment gas. 
     The airbag  100  may thus be fed to the outside from the retainer  51  and start to be deployed, finally being deployed into a shape illustrated in  FIG.  2   . 
     Thereafter, the flow may proceed to step S 03 . 
     [Step S 03 : Detection of Door Internal Pressure and Tensile Load] 
     The airbag control unit  210  may detect the pressure inside the door and the tensile load on the second air chamber  120 , with the use of the door internal pressure sensor  214  and the tensile load sensor  215 . 
     Thereafter, the flow may proceed to step S 04 . 
     [Step S 04 : Determination of Increase in Door Internal Pressure etc.] 
     The airbag control unit  210  may determine whether one or both of the pressure inside the door and the tensile load on the second air chamber  120  detected in step S 03  has increased to a preset threshold or more. 
     If one or both of the pressure and the tensile load becomes the threshold or more (step S 04 : Y), the flow may proceed to step S 05 . Otherwise (step S 04 : N), the flow may return to step S 03 , and the subsequent processes may be repeated. 
     [Step S 05 : Pressure Reduction in Second Air Chamber] 
     The airbag control unit  210  may release a portion of the deployment gas to the outside from the inside of the second air chamber  120 , by temporarily putting the pressure regulating valve  212  into an open state and thereafter returning the pressure regulating valve  212  to a closed state, to reduce the internal pressure of the second air chamber  120  to a predetermined post-collision internal pressure lower than a during-deployment internal pressure. 
     At this time, the airbag control unit  210  may perform feedback control on the pressure regulating valve  212  on the basis of the output of the internal pressure sensor  213 . 
     Thereafter, the series of processes may be ended and the flow may return, 
       FIG.  5    is a cross-sectional view of a state after a side collision in the vehicle including the airbag device according to the first example embodiment. 
     In  FIG.  5   , a solid line indicates, for example, the front side door  30  and the airbag  100  after the collision in the first example embodiment, and a dashed line indicates, for example, the front side door  30  after the collision assumed in a case where the airbag  100  is not provided. 
     As illustrated in  FIG.  5   , in the first example embodiment, a load F applied upon a side collision with an object such as the other vehicle V may be transmitted to the vehicle body in a distributed manner as a load F1 on the front side door  30  and a load F2 on the side sill  50 . This makes it possible to reduce the load F1 transmitted to the front side door  30 , making it possible to reduce the amount of deformation of the front side door  30  and an amount of movement of the front side door  30  to the inside of the vehicle compartment, as compared with the assumed case where the airbag  100  described above is not provided. 
     For example, it is possible to suppress displacement of a lower end of the front side door  30  to the vehicle-widthwise inside beyond the side sill  50 . 
     According to the first example embodiment described above, it is possible to achieve the following example effects. 
     (1) The first air chamber  110  of the airbag  100  transmits a load applied from the vehicle-widthwise outside to the side surface of the side sill  50  upon a side collision of the vehicle  1 . This makes it possible to suppress deformation of the front side door  30  entering the inside of the vehicle compartment  10 , making it possible to suppress damage to an occupant. 
     In addition, the internal pressure of the second air chamber  120  coupling the first air chamber  110  and the side sill  50  is controlled depending on the load application state from the airbag  100  to the vehicle body. This makes it possible to control a behavior of the airbag  100  to allow the first air chamber  110  to reliably transmit the load to the side sill  50 , which helps to more effectively achieve the example effects described above. 
     (2) It is possible to absorb collision energy applied above the first air chamber  110  upon the collision with the object by contraction of the third air chamber  130 , making it possible to suppress deformation of the front side door  30  above the first air chamber  110 .
 
(3) The internal pressure of the second air chamber  120  may be reduced on the basis of the output of the door internal pressure sensor  214  that detects the amount of deformation of the front side door  30 . Thus, in a case where load transmission from the first air chamber  110  to the front side door  30  is started and the amount of deformation of the front side door  30  increases, it is possible to reduce the internal pressure of the second air chamber  120  to promote deformation of the airbag  100  to wrap around the side sill  50 , to cause the first air chamber  110  to transmit a load diagonally downward to the side sill  50 . This promotes the load transmission to the side sill  50 , making it possible to suppress the amount of deformation of the front side door  30 .
 
     Second Example Embodiment 
     A description is given next of an airbag device according to a second example embodiment of the disclosure. 
     In the second example embodiment, portions common to those in the first example embodiment described above are denoted with the same reference numerals to avoid repetitive description, and differences will mainly be described. 
       FIG.  6    is a cross-sectional view of surroundings of the front side door in the vehicle including the airbag device according to the second example embodiment of the disclosure. 
     As illustrated in  FIG.  6   , in the second example embodiment, the airbag  100  may further include a buffer air chamber  140 . 
     The buffer air chamber  140  may be deployed in a state of being held between the lower part of the side sill  50  and a road surface G, in a region on the vehicle-widthwise inside with respect to the second air chamber  120 . 
     The buffer air chamber  140  may be provided with a control valve  141 . 
     The control valve  141  may be configured to, in response to a command from the airbag control unit  210 , switch between an open state that allows communication between the buffer air chamber  140  and the second air chamber  120  and a closed state that blocks the communication. 
     The control valve  141  may cooperate with the airbag control unit  210  to serve as a “communication controller” in one embodiment. 
     In response to establishment of pre-crash determination, the buffer air chamber  140  may receive the deployment gas supplied from the inflator  211  to be deployed at the same time as the first air chamber  110 , the second air chamber  120 , and the third air chamber  130 . 
     When deployment is completed, an internal pressure of the buffer air chamber  140  may be set to be a lower pressure than the internal pressure of the second air chamber  120 . 
     In the second example embodiment, pressure reduction in the second air chamber  120  after collision may be performed by opening the control valve  141  and moving a portion of the deployment gas inside the second air chamber  120  to the buffer air chamber  140 . 
     According to the second example embodiment described above, it is possible to achieve example effects similar to those of the first example embodiment described above. In addition, even in a case where a load including a downward component is applied to, for example, the first air chamber  110  and the second air chamber  120  of the airbag  100  upon collision with an object, the buffer air chamber  140  is able to suppress downward displacement of a member such as the first air chamber  110  by using reaction force applied from the road surface G, making it possible to further stabilize load transmission to a member such as the side sill  50 . 
     In addition, the control valve  141  may control a communication state between the second air chamber  120  and the buffer air chamber  140 . This makes it possible to control the internal pressure of the second air chamber  120  with the use of a simple configuration. 
     Third Example Embodiment 
     A description is given next of an airbag device according to a third example embodiment of the disclosure. 
       FIG.  7    is a cross-sectional view of surroundings of the front side door in the vehicle including the airbag device according to the third example embodiment of the disclosure. 
     In the third example embodiment, the second air chamber  120  may be configured to be deployed in a state in which its underside comes into contact with the road surface G. 
     Also in the third example embodiment, it is possible to achieve example effects similar to those of the first and second example embodiments described above. 
     It is also possible to simplify a device configuration as compared with the configuration according to the second example embodiment. 
     Fourth Example Embodiment 
     A description is given next of an airbag device according to a fourth example embodiment of the disclosure. 
     The airbag device according to the fourth example embodiment may include an unillustrated application direction sensor. 
     The application direction sensor may be provided within the space between the outer panel  31  and the inner panel  32  of the front side door  30 , in a region overlapping with the first air chamber  110  of the airbag  100  as viewed in the vehicle widthwise direction. 
     The application direction sensor may be configured to detect an application direction of a load from the first air chamber  110  to the front side door  30 , for example, a downward component of the load. 
     In the airbag device according to the fourth example embodiment, after deployment of the airbag  100 , pressure reduction in the second air chamber  120  may be performed in response to an increase in the downward component of the load detected by the application direction sensor. 
     According to the fourth example embodiment described above, pressure may be reduced in the second air chamber  120  in response to an increase in the downward component of the load transmitted from the first air chamber  110 , for example, to the front side door  30 . This makes it possible to reduce the internal pressure of the second air chamber  120  in response to start of load transmission from the first air chamber  110  to the side sill  50 . This prevents inhibition of a behavior of the first air chamber  110  pressing the side sill  50  from a diagonal upper side, making it possible to further promote load transmission from the airbag  100  to the side sill  50 . 
     Modification Examples 
     Although some example embodiments of the disclosure have been described in the foregoing by way of example with reference to the accompanying drawings, the disclosure is by no means limited to the embodiments described above. It should be appreciated that modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. The disclosure is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof. 
     (1) Configurations of the airbag device and the vehicle may be changed as appropriate, without being limited to the example embodiments described above. 
     For example, shapes, structures, materials, manufacturing methods, numbers, arrangements, etc. of the members included in the airbag device and the vehicle may be changed as appropriate. 
     (2) A configuration of the airbag, an arrangement of the air chambers, etc. may be changed as appropriate, without being limited to the configurations according to the example embodiments. For example, the third air chamber may be omitted in a case where energy absorption at an upper part of the door is possible by another method. Another air chamber may be additionally provided in addition to the air chambers described above. Each air chamber may be further divided.
 
(3) A method of detecting a symptom of collision may be changed as appropriate without being limited to the method using the sensors in the example embodiments. For example, another type of sensor may be used in addition to or in place of the sensors in the example embodiments. In another example, a symptom of collision may be detected by inter-vehicle communication or road-to-vehicle communication.
 
(4) In the example embodiments, the container, e.g, the retainer  51 , that contains the undeployed airbag  100  may be provided inside the lower part of the side sill  50 , However, a place where the container is provided may be changed as appropriate, without being limited thereto. For example, the container may be provided on an underside of the floor panel, or inside a side step, which is an aerodynamic part with design provided on the side sill.
 
(5) Although the example embodiments describe the example effects related to suppression of deformation of the front side door, similar example effects are achievable also in relation to suppression of deformation of the rear side door.
 
     Although the example embodiments describe, as an example, the vehicle including the front side door and the rear side door, the disclosure may also be applied to a vehicle including only one door on each side surface of the vehicle body. 
     As described above, according to at least one embodiment of the disclosure, it is possible to provide an airbag device that suppresses collision damage upon a side collision. 
     Each of the airbag control unit  210  and the environment recognition unit  220  illustrated in  FIG.  3    is implementable by circuitry including at least one semiconductor integrated circuit such as at least one processor (e.g., a central processing unit (CPU)), at least one application specific integrated circuit (ASIC), and/or at least one field programmable gate array (FPGA). At least one processor is configurable, by reading instructions from at least one machine readable non-transitory tangible medium, to perform all or a part of functions of each of the airbag control unit  210  and the environment recognition unit  220 . Such a medium may take many forms, including, but not limited to, any type of magnetic medium such as a hard disk, any type of optical medium such as a CD and a DVD, any type of semiconductor memory (i.e., semiconductor circuit) such as a volatile memory and a non-volatile memory. The volatile memory may include a DRAM and an SRAM, and the nonvolatile memory may include a ROM and an NVRAM. The ASIC is an integrated circuit (IC) customized to perform, and the FPGA is an integrated circuit designed to be configured after manufacturing in order to perform, all or a part of the functions of each of The airbag control unit  210  and the environment recognition unit  220  illustrated in  FIG.  3   .