Patent Publication Number: US-2023158993-A1

Title: Airbag device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2021-190140 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 Patent No. 6740168 discloses that an airbag is deployed to the vehicle-widthwise outside from an impact beam, i.e., a door beam, disposed to extend in a front-rear direction inside a door. 
     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 an A pillar, a B pillar, a C pillar, a door, and a side sill. The A pillar, the B pillar, and the C pillar are structural members provided in order from a front side on a side surface of a vehicle body of the vehicle and extending in a vertical direction. The door is provided to be openable and closable at a door opening provided at one or both of a position between the A pillar and the B pillar and a position between the B pillar and the C pillar. The side sill is disposed along a lower edge of the door. The airbag device includes an airbag, a collision mode predictor, and a pressure controller. The airbag is configured to be deployed from a container to be disposed on a lower side of the side sill to a region on a vehicle-widthwise outside of the side surface of the vehicle body including the door, in response to a symptom of collision of an object with the side surface of the vehicle body. The airbag includes a first air chamber configured to be disposed mainly in front of the B pillar after being deployed and a second air chamber configured to be disposed mainly behind the B pillar after being deployed. The collision mode predictor is configured to predict a collision mode of the object with the vehicle. The pressure controller is configured to, based on the collision mode predicted by the collision mode predictor, increase or reduce one of an internal pressure of the first air chamber and an internal pressure of the second air chamber independently of the other internal pressure, or increase or reduce the internal pressure of the first air chamber and the internal pressure of the second air chamber independently of each other. 
    
    
     
       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 cross-sectional view taken in a direction of arrows III-Ill illustrated in  FIG.  1   . 
         FIG.  4    is a diagram illustrating a configuration of a control system for an airbag in the airbag device according to one example embodiment. 
         FIG.  5    is a flowchart illustrating an overview of airbag deployment control in the airbag device according to one example embodiment. 
         FIG.  6    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to one example embodiment, and illustrates a state in which a region behind a B pillar is subjected to a side collision at a large collision angle. 
         FIG.  7    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to one example embodiment, and illustrates a state in which a region behind the B pillar is subjected to a side collision at a small collision angle. 
         FIG.  8    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to one example embodiment, and illustrates a state in which a region in front of the B pillar is subjected to a side collision at a small collision angle. 
         FIG.  9    is a plan view of a vehicle including an airbag device according to one example embodiment of the disclosure as viewed from above the vehicle. 
         FIG.  10    is a schematic view of a configuration of a front-rear movement mechanism for a first air chamber and a second air chamber in an airbag device according to one example embodiment of the disclosure. 
         FIG.  11    is a flowchart illustrating an overview of airbag deployment control in the airbag device according to one example embodiment. 
         FIG.  12    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to one example embodiment, and illustrates a state in which a region behind a B pillar is subjected to a side collision from a diagonal rear side. 
         FIG.  13    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to one example embodiment, and illustrates a state in which a pole comes into a local side collision. 
     
    
    
     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 by the vehicle body structure. 
     Moreover, in a side collision, a deformation speed at which a door is pushed into a vehicle compartment 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, a load applied to an airbag is eventually applied to the vehicle body, and energy absorption thus greatly depends on crush of a vehicle body structure. 
     What is desired is to reduce collision damage to a vehicle and an occupant by obtaining the amount of energy absorption by another method, without depending only on crush of a vehicle body structure. 
     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   . 
       FIG.  3    is a cross-sectional view taken in a direction of arrows III-III illustrated in  FIG.  1   . 
     In the first example embodiment, a vehicle  1  may be, for example, 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 . 
     Although  FIG.  2    illustrates cross-sections of the front side door  30  and a first air chamber  110  of an airbag  100 , cross-sections of the rear side door  40  and a second air chamber  120  may also have a similar configuration. 
     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, i.e., a base of the airbag  100 , after the airbag  100  is deployed. 
     As illustrated in  FIG.  1    and  FIG.  3   , the airbag  100  may include the first air chamber  110 , the second air chamber  120 , and a partition  130 . 
     The first air chamber  110  may be a part included in a front part of the airbag  100 . 
     The second air chamber  120  may be a part included in a rear part of the airbag  100 . 
     The partition  130  may be provided inside the airbag  100  to separate the first air chamber  110  and the second air chamber  120 . 
     The first air chamber  110  may have a front end provided in front of the A pillar  60 . 
     The first air chamber  110  may have a rear end provided in the vicinity of the B pillar  70 . 
     The second air chamber  120  may have a front end continuous with the rear end of the first air chamber  110  in the vicinity of the B pillar  70 . 
     The second air chamber  120  may have a rear end provided behind the C pillar  80 . 
     An upper end of the first air chamber  110  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. 
     An upper end of the second air chamber  120  may be disposed to be positioned above an unillustrated rear door beam provided inside the rear side door  40 , in a region from a front end to a rear end of a seating surface of an unillustrated rear seat. 
     As illustrated in  FIG.  3   , in plan view as viewed from above the vehicle  1 , the partition  130  may be inclined with respect to the vehicle widthwise direction in such a manner that its end  131  on the vehicle-widthwise inside is on a vehicle front side with respect to its end  132  on the vehicle-widthwise outside. 
     The end  131  may be disposed on the vehicle front side, i.e., the A pillar  60  side, with respect to the B pillar  70 . 
     The end  132  may be disposed on a vehicle rear side, i.e., the C pillar  80  side, with respect to the B pillar  70 . 
     With such a configuration, a portion of the first air chamber  110  on the rear side, a portion of the second air chamber  120  on the front side, and the B pillar  70  may be disposed to overlap with each other as viewed in the vehicle widthwise direction. 
     The first air chamber  110  may be configured to transmit a load applied from an object such as another vehicle V to, for example, the front side door  30 , the A pillar  60 , the B pillar  70 , and the side sill  50  in a distributed manner. 
     The second air chamber  120  may be configured to transmit a load applied from an object such as the other vehicle V to, for example, the rear side door  40 , the B pillar  70 , the C pillar  80 , and the side sill  50  in a distributed manner. 
       FIG.  4    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  and internal pressures of the respective air chambers in a deployed state. 
     The airbag control unit  210  may be coupled to, for example, the inflator  211 , a first air chamber pressure regulating valve  212 , a second air chamber pressure regulating valve  213 , a first air chamber internal pressure sensor  214 , and a second air chamber internal pressure 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  and the second air chamber  120  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  and the second air chamber  120  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 first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213  may be provided in the first air chamber  110  and the second air chamber  120 , respectively. The first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213  may each be a control valve such as an electromagnetic valve that adjusts the internal pressure of the corresponding air chamber. 
     The first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213  may each be configured to be normally kept in a closed state, and to open in response to a command from the airbag control unit  210 , and release a portion of the deployment gas inside the corresponding air chamber to the outside to reduce the internal pressure of the air chamber. 
     The first air chamber internal pressure sensor  214  and the second air chamber internal pressure sensor  215  may be pressure sensors that detect the internal pressures of the first air chamber  110  and the second air chamber  120 . The internal pressure may be a pressure of the deployment gas. 
     Outputs of the first air chamber internal pressure sensor  214  and the second air chamber internal pressure sensor  215  may be transmitted to the airbag control unit  210 . 
     In airbag deployment control to be described later, the airbag control unit  210  may perform feedback control on the first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213  in such a manner that the internal pressures of the first air chamber  110  and the second air chamber  120  detected by the first air chamber internal pressure sensor  214  and the second air chamber internal pressure sensor  215  are set to predetermined target pressures. 
     The airbag control unit  210  may cooperate with the pressure regulating valves and the internal pressure sensors to serve as a “pressure controller” in one embodiment. 
     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. 
     In one embodiment, the environment recognition unit  220  may serve as a “collision mode predictor”. 
     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 side impact 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. 
     In the first example embodiment, the airbag  100  is deployed in response to establishment of side impact pre-crash determination, and the internal pressures of the first air chamber  110  and the second air chamber  120  are controlled independently depending on a predicted collision mode. 
     Such control of the airbag  100  is described below. 
       FIG.  5    is a flowchart illustrating an overview of the 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 : Side Impact 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  from a diagonal front side is unavoidable. 
     If the environment recognition unit  220  determines that the collision is unavoidable (step S 01 : Y), the environment recognition unit  220  may establish side impact 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 : Determination of Collision Angle] 
     The environment recognition unit  220  may estimate a collision angle θ (see  FIG.  6    to  FIG.  8    to be described later) immediately before the object such as the other vehicle V collides with the vehicle  1 , and compare the estimated collision angle θ with a preset threshold θth. 
     According to some embodiments described in the present specification, the appended claims, etc., a collision angle may refer to an angle, in plan view as viewed from above, formed by a straight line extending along the front-rear direction of the own vehicle and a straight line extending along a relative movement direction, with respect to the own vehicle, of an object that comes into collision. The collision angle may be equal to or greater than 0° and less than 90°. 
     If the collision angle θ is the threshold θth or greater (step S 02 : Y), the flow may proceed to step S 04 , Otherwise (step S 02 : N), the flow may proceed to step S 03 . 
     [Step S 03 : Determination of Collision Position] 
     The environment recognition unit  220  may estimate a position where the other vehicle V collides with the airbag  100 , and determine whether the position (hereinafter referred to as a “collision position”) is, in the vehicle front-rear direction, in front of the B pillar  70 . The collision position may typically be a center position of a load F applied to the airbag  100  by the collision. 
     If the collision position is in front of the B pillar  70  (step S 03 : Y), the flow may proceed to step SOS. Otherwise, i.e., if the collision position is in a region including the B pillar  70  or further behind the B pillar  70  (step S 03 : N), the flow may proceed to step S 04 . 
     [Step S 04 : Airbag Deployment (Low Pressure on Front Side and High Pressure on Rear Side)] 
     The airbag control unit  210  may activate the inflator  211  to generate the deployment gas and supply the deployment gas to the first air chamber  110  and the second air chamber  120 , to thereby feed and deploy the airbag  100  from the retainer  51 . 
     At this time, the internal pressure of the first air chamber  110  may be set to a lower pressure than the internal pressure of the second air chamber  120  to allow the first air chamber  110  to have a relatively low pressure and the second air chamber  120  to have a relatively high pressure. 
     In this case, the second air chamber  120  may not be subjected to pressure reduction by the second air chamber pressure regulating valve  213 . 
     For the first air chamber  110 , the first air chamber pressure regulating valve  212  may be kept in an open state at a predetermined opening degree. 
     Thus, upon receiving the load applied by the collision, the first air chamber  110  is able to contract while exhausting the internal deployment gas from the first air chamber pressure regulating valve  212  to absorb energy. 
     Thereafter, the series of processes may be ended and the flow may return. 
     [Step S 05 : Airbag Deployment (Equal Pressures on Front and Rear Sides)] 
     The airbag control unit  210  may activate the inflator  211  to generate the deployment gas and supply the deployment gas to the first air chamber  110  and the second air chamber  120 , to thereby feed and deploy the airbag  100  from the retainer  51 . 
     At this time, the internal pressures of the first air chamber  110  and the second air chamber  120  may be set to a high pressure equal to the internal pressure of the second air chamber  120  in step S 04 . 
     In this case, the first air chamber  110  and the second air chamber  120  may not be subjected to pressure reduction by the first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213 . 
     Thereafter, the series of processes may be ended and the flow may return. 
     Described below are a state and example effects after a side collision in the vehicle including the airbag device according to the first example embodiment. 
       FIG.  6    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to the first example embodiment, and illustrates a state in which a region behind the B pillar is subjected to a side collision at a large collision angle. 
     In this case, the first air chamber  110  may be made to have a lower pressure than the second air chamber  120  (step S 04 ). 
     The other vehicle V may collide mainly with the second air chamber  120  from the diagonal front side at a collision angle θ greater than the predetermined threshold θth, and transmit the load F to, for example, the rear side door  40 , the B pillar  70 , the C pillar  80 , and the side sill  50  via the second air chamber  120 . 
     This generates, on the vehicle  1 , a moment M that causes a rear part of the vehicle body to swing to a side opposite to a collision side. The side opposite to the collision side may be, for example, a right side because the vehicle  1  is subjected to the collision from a left side in  FIG.  6   . 
     The moment M may cause the vehicle  1  to exhibit a yaw behavior in a spin mode around the vicinity of the power unit compartment  20  carrying a heavy object. 
     Energy applied to the vehicle body by the collision may partly be consumed by being converted into kinetic energy caused by such a yaw behavior and frictional energy caused by tire slip. This reduces the energy to be absorbed by, for example, crush of the vehicle body, suppressing damage to and deformation of the vehicle compartment  10 . 
     In addition, setting the internal pressure of the first air chamber  110  to a lower pressure than the internal pressure of the second air chamber  120  makes it possible to suppress attack from the first air chamber  110  to the vehicle body. 
       FIG.  7    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to the first example embodiment, and illustrates a state in which a region behind the B pillar is subjected to a side collision at a small collision angle. 
     In this case, the first air chamber  110  may be made to have a lower pressure than the second air chamber  120  (step S 04 ). 
     The other vehicle V may collide mainly with the second air chamber  120  from the diagonal front side at a collision angle θ less than the predetermined threshold θth, and transmit the load F to, for example, the rear side door  40 , the B pillar  70 , the C pillar  80 , and the side sill  50  via the second air chamber  120 . 
     This may cause the vehicle  1  to exhibit a behavior in which the vehicle body makes a translational motion to the side opposite to the collision side in the vehicle widthwise direction. The translational motion may typically be side slip. 
     Energy applied to the vehicle body by the collision may partly be consumed by being converted into kinetic energy caused by such a lateral translational motion of the vehicle body and frictional energy caused by tire slip. This reduces the energy to be absorbed by, for example, crush of the vehicle body, suppressing damage to and deformation of the vehicle compartment  10 . 
     In addition, setting the internal pressure of the first air chamber  110  to a lower pressure than the internal pressure of the second air chamber  120  makes it possible to suppress attack from the first air chamber  110  to the vehicle body. 
       FIG.  8    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to the first example embodiment, and illustrates a state in which a region in front of the B pillar is subjected to a side collision at a small collision angle. 
     In this case, the first air chamber  110  and the second air chamber  120  may be made to have equal pressures, e.g., equal high pressures (step S 05 ). 
     The other vehicle V may collide mainly with the first air chamber  110  from the diagonal front side at a collision angle θ less, or shallower, than the predetermined threshold θth. 
     At this time, a front end of the other vehicle V may slip to the rear side of the vehicle  1  sequentially along surfaces of the first air chamber  110  and the second air chamber  120  on the vehicle-widthwise outside, and a traveling direction of the other vehicle V may thus change to a direction in which the other vehicle V passes the vehicle  1 . 
     In this case, the load F transmitted from the airbag  100  to the vehicle  1  may be received by, for example, the A pillar  60 , the B pillar  70 , and the C pillar  80 . 
     Causing the other vehicle V to exhibit a behavior of passing the vehicle  1  makes it possible to suppress direct collision between the other vehicle V and the vehicle body of the vehicle  1 , and reduce energy applied from the other vehicle V to the vehicle body of the vehicle  1 . This reduces the energy to be absorbed by, for example, crush of the vehicle body, suppressing damage to and deformation of the vehicle compartment  10 . 
     According to the first example embodiment described above, it is possible to achieve the following example effects. 
     (1) The internal pressure of the first air chamber  110  and the internal pressure of the second air chamber  120  are controlled independently depending on the collision mode of an object such as the other vehicle V with the vehicle  1 . Thus, a form of load application from the object such as the other vehicle V to the vehicle body may be controlled to cause one or both of the vehicle body and the object to exhibit a behavior that reduces collision damage. This makes it possible to consume a portion of the energy caused by the collision as kinetic energy, thereby reducing the energy absorbed by, for example, crush of the vehicle body. This helps to suppress damage to and deformation of the vehicle body to keep survival space for an occupant.
 
(2) In a case where a side collision at the collision angle θ equal to or greater than the threshold θth with a region including the B pillar  70  on the side surface of the vehicle body is predicted, the internal pressure of the second air chamber  120  may be set to a higher pressure than the internal pressure of the first air chamber  110 . This promotes load transmission from the second air chamber  120  to a region of the vehicle body behind the B pillar  70 , causing a yaw behavior, typically a behavior in the spin mode, in which the rear part of the vehicle body swings to the side opposite to the collision side. This makes it possible to convert a portion of the energy applied by the collision into kinetic energy of the vehicle body and frictional energy caused by tire slip, and consume the energy.
 
     In addition, setting the internal pressure of the first air chamber  110  to a lower pressure than the internal pressure of the second air chamber  120  makes it possible to suppress attack to a front half part of the vehicle body, reducing damage to and deformation of the vehicle body. 
     For example, it is possible to suppress deformation of the front side door  30  resulting in entry into the vehicle compartment  10  beyond the side sill  50 . 
     (3) In a case where a collision from the diagonal front side at the collision angle θ less than the threshold θth with a region in front of the B pillar  70  on the side surface of the vehicle body is predicted, the internal pressure of the first air chamber  110  may be set to a high pressure equal to the internal pressure of the second air chamber  120 . This makes it possible to slide the object such as the other vehicle V to the rear side of the vehicle  1  along a surface of the airbag  100 , by using strength of, for example, the B pillar  70  of the vehicle body as reaction force, to guide the object such as the other vehicle V to pass the vehicle  1 . This makes it possible to prevent the vehicle body of the vehicle  1  and the object such as the other vehicle V from coming into direct collision.
 
(4) In a case where a collision from the diagonal front side at the collision angle θ less than the threshold θth with a region behind the B pillar  70  on the side surface of the vehicle body is predicted, the internal pressure of the second air chamber  120  may be set to a higher pressure than the internal pressure of the first air chamber  110 . This makes it possible to convert torsional load application to the B pillar  70  into compressive load application, and transmit the load applied by the collision to the B pillar  70  and the C pillar  80  in a distributed manner, to cause a behavior, typically a side slip behavior, of the vehicle  1  being pushed out laterally by the object such as the other vehicle V. This makes it possible to convert a portion of the energy applied by the collision into kinetic energy of the vehicle body and frictional energy caused by tire slip, and consume the energy.
 
     In addition, setting the internal pressure of the first air chamber  110  to a lower pressure than the internal pressure of the second air chamber  120  makes it possible to suppress attack to the front half part of the vehicle body, reducing damage to and deformation of the vehicle body. This also helps to prevent inhibition of deformation of the second air chamber  120  being compressed to be elongated in the front-rear direction, making it possible to transmit the load more effectively from the second air chamber  120  to the B pillar  70 . 
     (5) The partition  130  between the first air chamber  110  and the second air chamber  120  may be inclined with respect to the vehicle widthwise direction to allow a rear part of the first air chamber  110  and a front part of the second air chamber  120  to overlap with the B pillar  70  as viewed in the vehicle widthwise direction. This makes it possible to effectively transmit the load from both the first air chamber  110  and the second air chamber  120  to the B pillar  70 . 
     Second Example Embodiment 
     A description is given next of an airbag device according to a second example embodiment of the disclosure. 
     In example embodiments described below, portions common to those in the foregoing example embodiment are denoted with the same reference numerals to avoid repetitive description, and differences will mainly be described. 
     As illustrated in  FIG.  9   , in the airbag device according to the second example embodiment, the partition  130  separating the first air chamber  110  and the second air chamber  120  may be disposed along the vehicle widthwise direction in plan view as viewed from above the vehicle. 
     The partition  130  may be positioned, in the vehicle front-rear direction, to overlap with an intermediate part of the B pillar  70  in the vehicle front-rear direction. 
     Also in the second example embodiment described above, it is possible to achieve example effects similar to those of the first example embodiment described above, excluding the example effect described in the item (5). 
     Third Example Embodiment 
     A description is given next of an airbag device according to a third example embodiment of the disclosure. 
     In the airbag device according to the third example embodiment, the first air chamber  110  and the second air chamber  120  of the deployed airbag  100  may be movable in the front-rear direction with respect to the vehicle body by using a front-rear movement mechanism  300  described below. 
     The front-rear movement mechanism  300  may cooperate with the airbag control unit  210  to serve as an “airbag mover” in one embodiment. 
       FIG.  10    is a schematic view of a configuration of the front-rear movement mechanism  300  for the first air chamber  110  and the second air chamber  120  in the airbag device according to the third example embodiment. 
     In the third example embodiment, the retainer  51  may be divided into a front retainer  51 F and a rear retainer  51 R. 
     The first air chamber  110  and the second air chamber  120  may be independent bags, and each air chamber may be provided with the corresponding inflator  211 . 
     Before establishment of pre-crash determination for the vehicle  1 , the first air chamber  110  and the second air chamber  120  may be contained in a folded state in the front retainer  51 F and the rear retainer  51 R, respectively. 
     The front-rear movement mechanism  300  may include, for example, a rail  310 , pulleys  321  to  324 , and wires  331  to  334 . 
     The rail  310  may be a guide member provided inside the side sill  50  and disposed along the longitudinal direction of the side sill  50 , i.e., the vehicle front-rear direction. 
     The front retainer  51 F and the rear retainer  51 R may be supported by the rail  310  to be displaceable along a longitudinal direction of the rail  310  with respect to the side sill  50 . 
     The pulley  321  may be provided in the vicinity of the front end of the side sill  50 , and coupled to the front retainer  51 F via the wire  331 . 
     The pulley  321  may be configured to pull the front retainer  51 F to the vehicle front side by winding the wire  331 . 
     The pulley  322  may be provided in the vicinity of the front end of the side sill  50 , and coupled to the rear retainer  51 R via the wire  332 . 
     The pulley  322  may be configured to pull the rear retainer  51 R to the vehicle front side by winding the wire  332 . 
     The pulley  323  may be provided in the vicinity of the rear end of the side sill  50 , and coupled to the front retainer  51 F via the wire  333 . 
     The pulley  323  may be configured to pull the front retainer  51 F to the vehicle rear side by winding the wire  333 . 
     The pulley  324  may be provided in the vicinity of the rear end of the side sill  50 , and coupled to the rear retainer  51 R via the wire  334 . 
     The pulley  324  may be configured to pull the rear retainer  51 R to the vehicle rear side by winding the wire  334 . 
     The pulleys  321  to  324  may each be provided with an actuator, such as an electric motor, to be used to wind the corresponding wire. 
     The actuators may be controlled in response to a command from the airbag control unit  210 . 
     A description is given below of airbag deployment control and front-rear direction drive control in the third example embodiment. 
       FIG.  11    is a flowchart illustrating an overview of the airbag deployment control in the airbag device according to the third example embodiment. 
     The flow is described below in order of step. 
     [Step S 11 : Side Impact 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 the side surface of the vehicle  1  from the diagonal front side or a diagonal rear side is unavoidable. 
     If the environment recognition unit  220  determines that the collision is unavoidable (step S 11 : Y), the environment recognition unit  220  may establish side impact pre-crash determination, and the flow may proceed to step S 12 . Otherwise (step S 11 : N), the flow may proceed to step S 20 . 
     [Step S 12 : Determination of Diagonal Rear Collision] 
     The environment recognition unit  220  may determine whether the collision of the object such as the other vehicle V for which the pre-crash determination has been established is a diagonal rear collision in which the object collides with the vehicle  1  from the diagonal rear side. 
     If the collision is a diagonal rear collision (step S 12 : Y), the flow may proceed to step S 18 . Otherwise, i.e., if the collision is a side collision from the diagonal front side or the vehicle widthwise direction (step S 12 : N), the flow may proceed to step S 13 . 
     [Step S 13 : Determination of Collision Angle] 
     The environment recognition unit  220  may estimate a collision angle θ immediately before the object such as the other vehicle V collides with the own vehicle, and compare the estimated collision angle θ with a preset threshold θth. 
     If the collision angle θ is the threshold θth or greater (step S 13 : Y), the flow may proceed to step S 15 . Otherwise (step S 13 : N), the flow may proceed to step S 14 . 
     [Step S 14 : Determination of Collision Position] 
     The environment recognition unit  220  may estimate a collision position where the other vehicle V collides with the airbag  100 , and determine whether the collision position is, in the vehicle front-rear direction, in front of the B pillar  70 . 
     If the collision position is in front of the B pillar  70  (step S 14 : Y), the flow may proceed to step S 16 . Otherwise, i.e., if the collision position is in a region including the B pillar  70  (step S 14 : N), the flow may proceed to step S 15 . 
     [Step S 15 : Airbag Deployment (Low Pressure on Front Side and High Pressure on Rear Side)] 
     The airbag control unit  210  may activate the inflator  211  to generate the deployment gas and supply the deployment gas to the first air chamber  110  and the second air chamber  120 , to thereby feed and deploy the first air chamber  110  and the second air chamber  120  of the airbag  100  from the front retainer  51 F and the rear retainer  51 R. 
     At this time, the internal pressure of the first air chamber  110  may be set to a lower pressure than the internal pressure of the second air chamber  120  to allow the first air chamber  110  to have a relatively low pressure and the second air chamber  120  to have a relatively high pressure. 
     In this case, the second air chamber  120  may not be subjected to pressure reduction by the second air chamber pressure regulating valve  213 . 
     For the first air chamber  110 , the first air chamber pressure regulating valve  212  may be kept in an open state at a predetermined opening degree. 
     Thus, upon receiving the load applied by the collision, the first air chamber  110  is able to contract while exhausting the internal deployment gas from the first air chamber pressure regulating valve  212  to absorb energy. 
     Thereafter, the flow may proceed to step S 17 . 
     [Step S 16 : Airbag Deployment (Equal Pressures on Front and Rear Sides)] 
     The airbag control unit  210  may activate the inflator  211  to generate the deployment gas and supply the deployment gas to the first air chamber  110  and the second air chamber  120 , to thereby feed and deploy the first air chamber  110  and the second air chamber  120  of the airbag  100  from the front retainer  51 F and the rear retainer  51 R. 
     At this time, the internal pressures of the first air chamber  110  and the second air chamber  120  may be set equal to the internal pressure of the second air chamber  120  in step S 15 . 
     In this case, the first air chamber  110  and the second air chamber  120  may not be subjected to pressure reduction by the first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213 . 
     Thereafter, the flow may proceed to step S 17 . 
     [Step S 17 : Execution of Airbag Forward Movement Control] 
     The airbag control unit  210  may perform airbag forward movement control of giving a command to the actuators of the front-rear movement mechanism  300  to displace the first air chamber  110  and the second air chamber  120  of the airbag  100  to the front side with respect to the vehicle body of the vehicle  1 . 
     Positions of the first air chamber  110  and the second air chamber  120  after completion of the displacement may be, for example, matched with positions of the first air chamber  110  and the second air chamber  120  in the airbag device according to the first example embodiment. 
     Thereafter, the series of processes may be ended. 
     By the control described above, in a case where an object such as the other vehicle V comes into side collision from the diagonal front side or the side of the vehicle  1 , it is possible to achieve example effects similar to the example effects described with reference to  FIG.  6    to  FIG.  8    in the first example embodiment. 
     [Step S 18 : Airbag Deployment (Low Pressure on Front Side and High Pressure on Rear Side)] 
     The airbag control unit  210  may activate the inflator  211  to generate the deployment gas and supply the deployment gas to the first air chamber  110  and the second air chamber  120 , to thereby feed and deploy the first air chamber  110  and the second air chamber  120  of the airbag  100  from the front retainer  51 F and the rear retainer  51 R. 
     At this time, the internal pressure of the first air chamber  110  may be set to a lower pressure than the internal pressure of the second air chamber  120  to allow the first air chamber  110  to have a relatively low pressure and the second air chamber  120  to have a relatively high pressure. 
     Thereafter, the flow may proceed to step S 19 . 
     [Step S 19 : Execution of Airbag Rearward Movement Control] 
     The airbag control unit  210  may perform airbag rearward movement control of giving a command to the actuators of the front-rear movement mechanism  300  to displace the first air chamber  110  and the second air chamber  120  of the airbag  100  to the rear side with respect to the vehicle body of the vehicle  1 . 
     An amount of the displacement may be set to allow movement to the rearmost end of a movable range of the front retainer  51 F and the rear retainer  51 R. In another example, the control may be performed to allow movement to an intermediate position within the movable range, depending on the collision position of the object such as the other vehicle V detected by the environment recognition unit  220 . 
     Thereafter, the series of processes may be ended. 
     [Step S 20 : Local Collision Determination] 
     The environment recognition unit  220  may estimate the possibility of the vehicle  1  slipping sideway and departing from a lane, for example, to collide with a relatively small object that can cause local damage to the vehicle body on the side surface of the vehicle body. Non-limiting examples of the relatively small object may include poles, such as a traffic light pole or a utility pole, and a tree. 
     If the possibility of such a collision is a predetermined value or more (step S 20 : Y), the environment recognition unit  220  may establish local collision determination, and the flow may proceed to step S 21 . Otherwise (step S 20 : N), the series of processes may be ended. 
     [Step S 21 : Airbag Deployment (Equal Pressures on Front and Rear Sides)] 
     The airbag control unit  210  may activate the inflator  211  to generate the deployment gas and supply the deployment gas to the first air chamber  110  and the second air chamber  120 , to thereby feed and deploy the first air chamber  110  and the second air chamber  120  of the airbag  100  from the front retainer  51 F and the rear retainer  51 R. 
     At this time, the internal pressures of the first air chamber  110  and the second air chamber  120  may be set equal to the internal pressure of the second air chamber  120  in step S 15 . 
     In this case, the first air chamber  110  and the second air chamber  120  may not be subjected to pressure reduction by the first air chamber pressure regulating valve  212  and the second air chamber pressure regulating valve  213 . 
     Thereafter, the flow may proceed to step S 22 . 
     [Step S 22 : Collision Position Following Control] 
     The airbag control unit  210  may execute collision position following control of giving a command to the actuators of the front-rear movement mechanism  300  to move the first air chamber  110  and the second air chamber  120  in the front-rear direction with respect to the side sill  50 , to allow one or both of the first air chamber  110  and the second air chamber  120  of the airbag  100  to cover the collision position of the object, such as a pole, with the vehicle body estimated by the environment recognition unit  220 . 
     Thereafter, the series of processes may be ended. 
     Described below are a state and example effects after a side collision in the vehicle including the airbag device according to the third example embodiment. 
     As described above, example effects achieved in a case where the vehicle  1  is subjected to a side collision with an object such as the other vehicle V from the diagonal front side may be similar to the example effects of the first example embodiment described with reference to  FIG.  6    to  FIG.  8   . 
       FIG.  12    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to the third example embodiment, and illustrates a state in which a region behind the B pillar is subjected to a side collision from the diagonal rear side. 
     In this case, the first air chamber  110  may be made to have a lower pressure than the second air chamber  120  (step S 18 ). 
     The other vehicle V may collide mainly with the second air chamber  120  from the diagonal rear side of the vehicle  1 , and transmit the load F to, for example, the rear side door  40 , the B pillar  70 , the C pillar  80 , and the side sill  50  via the second air chamber  120 . 
     This makes it possible to obtain a uniform load to strongly push the B pillar  70 , making it possible to effectively transmit the load F applied from the other vehicle V to the second air chamber  120  to a vehicle body structure such as the B pillar  70 . 
     This reduces local deformation of the rear side door  40 , making it possible to suppress deformation of the rear side door  40  resulting in entry into the vehicle compartment  10 . 
       FIG.  13    is a schematic view of a state immediately after collision of the vehicle including the airbag device according to the third example embodiment, and illustrates a state in which a pole comes into a local side collision. 
     In this case, the first air chamber  110  and the second air chamber  120  may be made to have equal pressures, e.g., equal high pressures (step S 21 ). 
     For example, a pole P such as a utility pole or a traffic light pole may collide with the vehicle  1  toward the vicinity of the middle part of the front side door  30  from the diagonal front side of the vehicle  1 , due to lane departure involving side slip of the vehicle  1 . 
     For this collision, the airbag  100  may be moved forward by the front-rear movement mechanism  300  into a state in which the pole P collides with a middle part of the first air chamber  110 . 
     The load applied from the pole P to the first air chamber  110  may be transmitted to, for example, the A pillar  60 , the B pillar  70 , the side sill  50 , and the front side door  30  in a distributed manner via the first air chamber  110 . 
     This suppresses great local deformation of the front side door  30 , making it possible to reduce damage to an occupant due to entry of the front side door  30  into the vehicle compartment  10 . 
     As described above, according to the third example embodiment, it is possible to achieve example effects similar to those of the first example embodiment described above. In addition, the first air chamber  110  and the second air chamber  120  of the airbag  100  may be moved in the front-rear direction with respect to the vehicle body by the front-rear movement mechanism  300 . This makes it possible to transmit the load from the object to the vehicle body more accurately, making it possible to promote the example effects described above. 
     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) The control of the internal pressures of the first air chamber and the second air chamber depending on the collision mode in each of the example embodiments is an example, and may be changed as appropriate.
 
     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.  4    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.  4   .