Patent Publication Number: US-2022212620-A1

Title: Roof airbag for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Korean Patent Application No. 10-2021-0000920, filed Jan. 5, 2021, and Korean Patent Application No. 10-2021-0003459, filed Jan. 11, 2021, the entire content of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a roof airbag for a vehicle, the roof airbag having an airbag cushion configured to be unfolded downward from an inner roof to protect a passenger seated on a seat. 
     2. Discussion of Related Art 
     In general, safety devices are installed in vehicles to protect passengers from accidents such as collisions and rollovers. As such safety devices, there are seat belts that restrain the body of a passenger and airbags that mitigate an impact of the passenger hitting the vehicle. The airbags are variously provided in various portions in the vehicle, such as a driver seat airbag provided in a steering wheel, a passenger seat airbag provided in an instrument panel of a passenger seat, etc. 
     Meanwhile, a vehicle is divided into a front space where front seat passengers are located and a rear space where rear seat passengers are located. In a vehicle collision, there is a problem in that the rear seat passengers are moved forward by inertia to cause a collision between the passengers in the vehicle. 
     Recently, self-driving vehicles are increasing, and the self-driving vehicles are configured to variously adjust a position of a seat within 360 degrees. Accordingly, the seat positions in the self-driving vehicles may be adjusted such that the front seat passengers and the rear seat passengers face each other. When a vehicle collision occurs while the front seat passengers and the rear seat passengers face each other, the passengers may be injured by a collision between the passengers. 
     The foregoing described as the controller and the controlling method of operating a fuel cell is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problem occurring in the related art, and the present invention is intended to provide a roof airbag for a vehicle, in which an airbag cushion is unfolded downward from an inner roof to protect a passenger seated on a seat and the airbag cushion is formed to be bent, so that a passenger is safely protected from an impact. 
     In order to achieve the above objective, according to one aspect of the present invention, there is provided a roof airbag for a vehicle, the roof airbag including: an airbag cushion configured to be inflated by a gas supplied from an inflator and to be unfolded downward from a roof; a main tether of which opposite ends are connected to opposite ends of the airbag cushion at a first surface of the airbag cushion, the main tether being extended shorter than a vertical length of the airbag cushion; and a sub-tether of which a first end is connected to the roof and a second end is connected to a second surface of the airbag cushion, wherein, when the airbag cushion is unfolded, the airbag cushion may be bent by the main tether, and the sub-tether may guide an unfolding direction of the airbag cushion. 
     The sub-tether may be extended shorter than a length of the main tether. 
     The sub-tether may be configured such that a connection position of the second end and an extended length of the sub-tether may be preset, so that a bent portion of the airbag cushion bent by the main tether in unfolding of the airbag cushion may be located at the body of a user seated on a seat. 
     The sub-tether may be configured to have an area covering some areas of the second surface or an entire area of the second surface of the airbag cushion. 
     The airbag cushion may be configured to be folded in a zigzag shape when the airbag cushion is folded before unfolding, and the sub-tether may be configured to cover the folded airbag cushion, and thus the sub-tether may be supported by the roof in unfolding of the airbag cushion to guide the airbag cushion so as to prevent the airbag cushion from being unfolded toward the roof. 
     The sub-tether may have a vertical length longer than a half of the vertical length of the airbag cushion. 
     The sub-tether may include a plurality of sub-tethers, and the second end of the sub-tether may be connected to each of the opposite side ends of the airbag cushion at the second surface of the airbag cushion. 
     The airbag cushion may be configured to be folded in a circular shape when being folded before unfolding, and the sub-tether may be connected to the side end of the airbag cushion, and thus unfolding of the airbag cushion may not interfere with the sub-tether. 
     The first end of the sub-tether may be connected to the roof while being spaced apart from the airbag cushion provided at the roof. 
     The airbag cushion may include a plurality of dead-lines by which the opposite surfaces of the airbag cushion may be attached to each other to block a flow of gas, the plurality of dead-lines being arranged to be spaced apart from each other along a longitudinal direction, as an inflated direction of the airbag cushion, and being extended in a transverse direction of the airbag cushion while opposite ends of each of the dead-lines may be spaced apart from the opposite side ends of the airbag cushion. 
     The plurality of dead-lines may be arranged to be spaced apart from each other at predetermined intervals along the longitudinal direction of the airbag cushion, and each interval between the dead-lines may be longer than an interval between one end of each of the dead-lines and one of the side ends of the airbag cushion. 
     The dead-lines may include divided lines, each of the divided lines being divided in the transversal direction of the airbag cushion, and the dead-lines may be configured to allow the gas to flow between the divided lines. 
     The dead-lines may include a first line portion and a second line portion, the first line portion being configured to allow the gas to flow between the divided lines divided in the transversal direction of the airbag cushion, and the second line portion being extended in the transversal direction of the airbag cushion. 
     The first line portion and the second line portion may be repeatedly arranged in an alternated manner in the longitudinal direction of the airbag cushion. 
     The dead-lines may be arranged such that the first line portion and the second line portion may be arranged in the longitudinal direction of the airbag cushion and then the first line portion may be repeatedly arranged. 
     One of a plurality of first line portions closest to the inflator in the airbag cushion may be extended such that an outer end of the divided line may be inclined in an inflated direction of the airbag cushion, and remaining first line portions may be extended such that inner ends of the divided line may be inclined in the inflated direction the airbag cushion. 
     The second line portion may be formed such that a center portion thereof may be bent toward the divided lines of the first line portion that may be closest to the inflator. 
     As described above, the roof airbag for a vehicle having the above-described structure has the airbag cushion configured to be unfolded downward from the inner roof to protect the passenger seated on the seat, and the airbag cushion is formed to be bent toward the passenger by the main tether and the sub-tether. Therefore, a restraining force for the passenger is secured and the passenger can be safely protected from an impact. Furthermore, the airbag cushion can be efficiently unfolded without insertion into the roof-side portion of the vehicle body and the headlining by the sub-tether. Specifically, the transversal contraction of the airbag cushion can be prevented and the unfolding shape of the airbag cushion can be maintained. Furthermore, the fluidity of the gas flow in the airbag cushion is secured, so that the airbag cushion can be rapidly unfolded. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objectives, features, and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view showing a roof airbag for a vehicle according to the present disclosure; 
         FIG. 2  is a view showing a roof airbag for a vehicle according to a first embodiment of the present disclosure; 
         FIG. 3  is a view showing folding of the airbag cushion according to the first embodiment of the present disclosure shown in  FIG. 2 ; 
         FIG. 4  is a view showing an airbag cushion according to a second embodiment of the present disclosure; 
         FIG. 5  is a view showing folding of the airbag cushion according to the second embodiment of the present disclosure shown in  FIG. 4 ; 
         FIG. 6  is a view showing dead-lines of the airbag cushion according to the first embodiment of the present disclosure; 
         FIG. 7  is a view showing dead-lines of the airbag cushion according to the second embodiment of the present disclosure; 
         FIG. 8  is a view showing dead-lines of an airbag cushion according to a third embodiment of the present disclosure; 
         FIG. 9  is a view showing dead-lines of an airbag cushion according to a fourth embodiment of the present disclosure; and 
         FIG. 10  is a view showing dead-lines of an airbag cushion according to a fifth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinbelow, a roof airbag for a vehicle according to exemplary embodiments of the present disclosure will be described with reference to accompanying drawings. 
       FIG. 1  is a view showing a roof airbag for a vehicle according to the present disclosure.  FIG. 2  is a view showing a roof airbag for a vehicle according to a first embodiment of the present disclosure.  FIG. 3  is a view showing folding of the airbag cushion according to the first embodiment of the present disclosure shown in  FIG. 2 .  FIG. 4  is a view showing an airbag cushion according to a second embodiment of the present disclosure.  FIG. 5  is a view showing folding of the airbag cushion according to the second embodiment of the present disclosure shown in  FIG. 4 . 
       FIG. 6  is a view showing dead-lines of the airbag cushion according to the first embodiment of the present disclosure.  FIG. 7  is a view showing dead-lines of the airbag cushion according to the second embodiment of the present disclosure.  FIG. 8  is a view showing dead-lines of an airbag cushion according to a third embodiment of the present disclosure.  FIG. 9  is a view showing dead-lines of an airbag cushion according to a fourth embodiment of the present disclosure.  FIG. 10  is a view showing dead-lines of an airbag cushion according to a fifth embodiment of the present disclosure. 
     According to the present disclosure, as shown in  FIG. 1 , the roof airbag for a vehicle includes: an airbag cushion  100  unfolded downward from a roof and arranged in front of a seat; a main tether  200  of which opposite ends are connected to opposite ends of the airbag cushion  100  at a first surface of the airbag cushion  100 , the main tether  200  being extended shorter than a vertical direction of the airbag cushion  100 ; and a sub-tether  300  of which a first end  310  is connected to the roof and a second end  320  is connected to a second surface of the airbag cushion  100 . 
     The airbag cushion  100  is provided an inside portion of the roof. The airbag cushion  100  may be supplied with inflation gas from an inflator I and may be unfolded downward from the roof and arranged between a plurality of seats. 
     The main tether  200  is connected to both the opposite ends of the airbag cushion  100  at the first surface of the airbag cushion  100 . When a plurality of airbag cushions  100  is provided, the main tether may be a surface on which the airbag cushions  100  face to each other. In the main tether  200 , as the main tether is formed shorter than the vertical direction of the airbag cushion  100 , the airbag cushion  100  is limited to be unfolded by the length of the main tether  200 , thus being bent. 
     Furthermore, the sub-tether  300  of which the first end  310  is connected to the roof and the second end  320  is connected to the second surface of the airbag cushion  100  is provided. The sub-tether  300  may be extended shorter than the length of the main tether  200 . Therefore, when the airbag cushion  100  is unfolded, the airbag cushion  100  is bent while the inflation of the airbag cushion  100  is limited by the length of the main tether  200 . As the sub-tether  300  guides a bending direction of the airbag cushion  100 , a bent portion of the airbag cushion  100  may be directed to the seat. 
     Accordingly, when a passenger seated on a seat touches the bent portion of the airbag cushion  100  in a vehicle collision, the airbag cushion  100  of the present disclosure may improve a restraining force for the passenger and protect the safety of the passenger from an impact of the vehicle collision. 
     In describing the present disclosure in detail, when the airbag cushion  100  is unfolded, the sub-tether  300  may be preset in a connection position of the second end  320  and an extension length of the sub-tether, so that the portion of the airbag cushion bent by the main tether  200  is positioned at a location corresponding to the body of the passenger seated on the seat. 
     The sub-tether  300  guides the bending direction of the airbag cushion  100  while the first end  310  of the sub-tether  300  is connected to the roof and the second end  320  is connected to the second surface of the airbag cushion  100 . Accordingly, based on a bent shape of the airbag cushion  100  bent by the main tether  200 , the connection position of the second end  320  of the sub-tether  300  connected to the airbag cushion  100  or the extension length of the sub-tether  300  is preset, so that the bent portion of the airbag cushion  100  is located at the body of the passenger seated on the seat. Therefore, the upper body of the passenger is placed on an upper portion  100   a  of the airbag cushion  100  on the basis of the bent portion of the airbag cushion  100 , and the lower body of the passenger is supported by a lower portion  100   b  of the airbag cushion  100  and may be safely protected. 
     Meanwhile, the first end  310  of the sub-tether  300  may be connected to the roof while being spaced apart from the airbag cushion  100  provided at the roof. By the arrangement of the sub-tether  300 , an unfolding shape of the airbag cushion  100  may be efficiently achieved. The sub-tether  300  may be prevented from being broken as the airbag cushion  100  in unfolding hits the sub-tether  300 . 
     Meanwhile, the sub-tether  300  of the present disclosure may be applied in various embodiments. 
     As a first example, as shown in  FIGS. 2 and 3 , the sub-tether  300  may be formed to have an area covering some areas or the entire area of the second surface of the airbag cushion  100 . Furthermore, a vertical length of the sub-tether  300  may be formed longer than a half of the vertical length of the airbag cushion  100 . 
     As described above, as the sub-tether  300  is formed to have the area covering the airbag cushion  100 , a coupling portion between the sub-tether  300  and the airbag cushion  100  is enlarged to allow the sub-tether  300  and the airbag cushion  100  to be connected to each other by a strong coupling force. Furthermore, as the vertical length of the sub-tether  300  is formed longer than a half of the vertical length of the airbag cushion  100 , the sub-tether  300  covers the airbag cushion  100  and a support force to the roof, which will be described below, may be secured. 
     On the basis of the bent portion of the airbag cushion  100 , the sub-tether  300  may be formed to partially cover a portion of the airbag cushion  100  corresponding to the upper portion  100   a  of the airbag cushion  100 , and may be formed to entirely cover a portion of the airbag cushion  100  corresponding to the lower portion  100   b  of the airbag cushion  100 . Therefore, the weight of the sub-tether  300  may be reduced, a coupling force may be increased by the secured area of the sub-tether  300 , and the support force to the roof may be secured. 
     In detail, the airbag cushion  100  is folded in a zigzag shape in folding before unfolding, and the sub-tether  300  covers the folded airbag cushion  100  thus guiding the airbag cushion  100  not to be unfolded toward the roof in unfolding of the airbag cushion  100  as the sub-tether  300  is supported by the roof. 
     As shown in  FIG. 1 , the airbag cushion  100  is provided to a roof-side portion of a vehicle body R with a housing U as a medium, and is not exposed to the inside of the vehicle by a headlining H before the airbag cushion  100  is unfolded. However, a gap exists between the roof-side portion of the vehicle body R and the headlining H, and when the airbag cushion  100  is unfolded, the airbag cushion  100  may be unfolded toward the gap between the roof-side vehicle body R and the headlining H. 
     Therefore, with the zigzag folded shape of the airbag cushion  100  when the airbag cushion is folded before unfolding, the airbag cushion may be efficiently unfolded downward from the roof. In addition, while the sub-tether  300  covers the folded airbag cushion  100 , the sub-tether  300  is supported by the headlining H located at the roof in unfolding of the airbag cushion  100 , and thus the airbag cushion  100  is prevented from being unfolded toward the gap between the roof-side vehicle body R and the headlining H. 
     Therefore, when the airbag cushion  100  is unfolded, the sub-tether  300  is supported by a roof-side portion of the headlining H and blocks the gap between the roof-side portion of the vehicle body R and the headlining H, whereby the airbag cushion  100  is prevented from being moved toward the gap between the roof-side portion of the vehicle body R and the headlining H and may be efficiently unfolded downward. Furthermore, the direction of the airbag cushion  100  bent by the sub-tether  300  is guided to be directed to the seat and thus the airbag cushion  100  may safely protect the passenger. 
     Meanwhile, in another embodiment, as shown in  FIGS. 4 and 5 , the sub-tether  300  includes a plurality of sub-tethers  300 , and second ends  320  of the sub-tethers  300  may be respectively connected to the opposite side ends of the airbag cushion  100  at the second surface of the airbag cushion  100 . 
     Therefore, as the plurality of sub-tethers  300  are connected to the opposite side ends of the airbag cushion  100  at the second surface of the airbag cushion  100 , the sub-tethers  300  and the airbag cushion  100  may be connected to each other by a strong coupling force. 
     Furthermore, the airbag cushion  100  is folded to be wrapped in a circular shape when being folded before unfolding and each of the sub-tethers  300  is connected to one side end of the airbag cushion  100 , so that unfolding of the airbag cushion  100  does not interfere. The airbag cushion  100  is wrapped such that one surface thereof is directed to the inside. Therefore, the airbag cushion  100  is released at the opposite side to the gap between the roof-side portion of the vehicle body R and the headlining H when the airbag cushion  100  is unfolded, the airbag cushion  100  avoids unfolding toward the gap between the roof-side portion of the vehicle body R and the headlining H. Furthermore, each of the sub-tethers  300  is connected to the one side end of the airbag cushion  100 , unfolding of the airbag cushion  100  does not interfere with the sub-tether  300 , so that the airbag cushion  100  may be efficiently unfolded downward from the roof 
     According to the present disclosure, the airbag cushion  100  includes a dead-line  110 , so that the shape of the airbag cushion  100  inflated by the gas supplied from the inflator I is maintained and the dead-line  110  guides a flow direction of the gas in the airbag cushion  100  to allow the airbag cushion  100  to be efficiently unfolded. 
     The dead-line  110  is a portion where the opposite surfaces of the airbag cushion  100  are attached to each other, and a flow of the gas is blocked at the portion with the dead-lines  110  in the airbag cushion  100 . The dead-line  110  includes a plurality of dead-lines  110  formed to be spaced apart from each other along a longitudinal direction of the airbag cushion  100 . The plurality of dead-lines  110  is extended in the transversal direction of the airbag cushion  100  such that opposite ends of each of the dead-lines  110  are respectively spaced apart from the opposite side ends of the airbag cushion  100 . Accordingly, the airbag cushion  100  is prevented from being contracted in the transversal direction by the dead-lines  110  extended in the transversal direction. In the conventional airbag cushion  100 , the dead-lines  110  are extended in the longitudinal direction of the airbag cushion, so that the conventional airbag cushion  100  is contracted in the longitudinal direction by the dead-lines  110 , thus the passenger seated on the seat cannot be sufficiently protected. However, as the dead-lines  110  are extended in the transversal direction of the airbag cushion  100  of the present disclosure, transversal contraction of the airbag cushion  100  is prevented, and a transversal width of the airbag cushion  100  is secured when the airbag cushion  100  is inflated, thereby safely protecting the passenger. Furthermore, each of the dead-lines  110  is extended in the transversal direction of the airbag cushion  100  such that the opposite ends of the dead-line  110  is spaced apart from the opposite side ends of the airbag cushion  100 . Therefore, the gas flows into gaps between the dead-lines  110  and the opposite side ends of the airbag cushion  100 , so that the airbag cushion  100  may be efficiently unfolded in the longitudinal direction. 
     According to the present disclosure, the dead-lines  110  may be applied to the airbag cushion  100  in various embodiments. 
     As the first embodiment, as shown in  FIG. 6 , the dead-lines  110  are arranged in the longitudinal direction of the airbag cushion  100  at predetermined intervals, each of the intervals between the dead-lines  110  is larger than an interval between one end of each of the dead-lines  110  and one side end of the airbag cushion  100 . 
     As described above, as the dead-lines  110  are arranged in the longitudinal direction of the airbag cushion  100  at the predetermined intervals, the overall shape of the airbag cushion  100  may be maintained by the dead-lines  110 . Even though the airbag cushion  100  is inflated, the transversal contraction of the airbag cushion  100  is limited by the dead-lines  110  arranged in the longitudinal direction of the airbag cushion  100 . 
     The interval a between one of the dead-lines  110  and another dead-line  110  may be formed larger than the interval b between the end of the dead-line and the side end of the airbag cushion  100 . Therefore, the airbag cushion  100  may be efficiently unfolded as the gas flows through the gap between the opposite ends of the airbag cushion and the opposite ends of the dead-lines  110 , and as the gas is moved into the intervals between the dead-lines  110  to inflate the airbag cushion  100 , the passenger can be protected from an impact. 
     Furthermore, when the intervals between the dead-lines  110  are formed smaller than the intervals between the ends of the dead-lines  110  and the side ends of the airbag cushion  100 , the intervals between the dead-lines  110  are narrowed and thus not safely protecting the passenger from an impact. As the side ends of the airbag cushion  100  are excessively inflated, the airbag cushion may not safely restrain the passenger. Therefore, the intervals between the dead-lines  110  is formed larger than the intervals between the ends of the dead-lines  110  and the side ends of the airbag cushion  100 . 
     As a second embodiment, as shown in  FIG. 7 , each of the dead-lines  110  may include divided lines  110   a  divided in the transversal direction of the airbag cushion  100 , thereby allowing the gas to flow through the divided lines  110   a.    
     As described above, as the dead-lines  110  includes the divided lines  110   a  divided in the transversal direction of the airbag cushion  100 , the gas flowing in the airbag cushion  100  may be flow through outsides of the divided lines  110   a  and gaps between the divided lines  110   a.  Each of the divided lines  110   a  may be divided at the center portion of the airbag cushion  100 , or may be divided on the basis of a portion where the gas is supplied from the inflator I. Therefore, even though the dead-lines  110  are provided in the airbag cushion  100 , the gas of the inflator I flows through the gaps between the divided lines  110   a  of the dead-lines  110 , so that the inflating speed of the airbag cushion  100  increases. Furthermore, as a flow of the gas is induced into the opposite sides of the airbag cushion  100  by the divided lines  110   a,  the airbag cushion  100  may rapidly achieve the inflated shape thereof. 
     Meanwhile, the dead-lines  110  may include first line portions  111  and second line portions  112 . The first line portions  111  are provided to allow the gas to flow between the divided lines  110   a  divided in the transversal direction of the airbag cushion  100 , and the second line portions  112  are extended in the transversal direction of the airbag cushion  100 . 
     As described above, as the first line portions  111  and the second line portions  112  are formed in the longitudinal direction of the airbag cushion  100 , inflating of the airbag cushion  100  is efficiently maintain, and the inflating speed of the airbag cushion  100  may be secured. 
     As the third embodiment described above, as shown in  FIG. 8 , the first line portions  111  and the second line portions  112  may be repeatedly arranged in an alternated manner in the longitudinal direction of the airbag cushion  100 . The first line portions  111  and the second line portions  112  may be repeatedly arranged in an order of the first line portions  111  and the second line portions  112  with the portion where the gas is supplied from the inflator I as a start point. 
     Therefore, when the gas of the inflator I is supplied into the airbag cushion  100 , the gas flows through the first line portions  111  of the divided lines  110   a,  so that initial unfolding speed of the airbag cushion  100  increases and thus the airbag cushion is rapidly unfolded from the roof to the interior of the vehicle. Furthermore, the gas passing through the first line portions  111  in the airbag cushion  100  is moved toward the sides of the airbag cushion  100  while flowing through the second line portions  112 . Therefore, while inflating of the airbag cushion  100  is partially achieved, the gas passes through the first line portions  111  and the second line portions  112  and then the airbag cushion  100  may be fully unfolded at a high speed. 
     Meanwhile, as a fourth embodiment, as shown in  FIG. 9 , the dead-lines  110  may be arranged such that the first line portions  111  and the second line portions  112  are provided in the longitudinal direction of the airbag cushion  100  and then the first line portions  111  are repeatedly arranged. 
     Therefore, when the gas of the inflator I is supplied into the airbag cushion  100 , the gas flows through the first line portions  111  of the divided lines  110   a,  so that initial unfolding speed of the airbag cushion  100  increases and thus the airbag cushion is rapidly unfolded from the roof to the interior of the vehicle. Furthermore, the gas passing through the first line portions  111  in the airbag cushion  100  is moved toward the sides of the airbag cushion  100  while flowing through the second line portions  112 . As described above, while inflating of the airbag cushion  100  is partially achieved, the gas passes through the first line portions  111  repeatedly arranged, and thus the airbag cushion  100  may be rapidly unfolded. In addition, as the first line portions  111  constitute the divided lines  110   a,  a flow of the gas is moved to both the center portion and opposite sides of the airbag cushion  100 , so that the airbag cushion  100  may be rapidly unfolded and precisely inflated. 
     Meanwhile, as a fifth embodiment, as shown in  FIG. 10 , among the plurality of first line portions  111 , a first line portion  111  located close to the inflator I in the airbag cushion  100  is extended with outer ends of the divided lines  110   a  inclined in an inflated direction of the airbag cushion  100  and remaining first line portions  111  is extended with an inner ends of the divided lines  110   a  inclined in the inflated direction of the airbag cushion  100 . 
     Furthermore, the second line portion  112  may be provided such that a center portion thereof is bent to be directed toward a gap between the divided lines  110   a  of the first line portion  111  closest to the inflator I. 
     Therefore, when the gas of the inflator I is supplied into the airbag cushion  100 , the gas flows through the first line portions  111  of the divided lines  110   a,  so that initial unfolding speed of the airbag cushion  100  increases and thus the airbag cushion is rapidly unfolded from the roof to the interior of the vehicle. Specifically, as the first line portion  111  closest to the inflator I is extended such that the outer ends of the divided lines  110   a  are inclined in the inflated direction of the airbag cushion  100 , a flow of the gas is induced in the inclined directions of the divided lines  110   a  and the airbag cushion  100  may be inflated at a high speed in both the transversal direction and the longitudinal direction of the airbag cushion  100 . 
     Then, the gas passing through the first line portions  111  closest to the inflator I in the airbag cushion  100  is moved toward the opposite sides of the airbag cushion  100  through the second line portion  112 , so that a transversally inflated state of the airbag cushion  100  may be maintained. As the second line portion  112  is provided such that the center portion thereof is bent to be directed toward the gap between the divided lines  110   a  of the first line portion  111  closest to the inflator I, the gas flowing through the gap between the divided lines  110   a  of the first line portion  111  is moved to the opposite sides of the airbag cushion  100  by a bent portion of the second line portion  112 , so that transversal unfolding of the airbag cushion  100  may be rapidly performed. 
     Meanwhile, as the remaining first line portions  111  arranged after the second line portions  112  are arranged such that the inner ends of the divided lines  110   a  are inclined in the inflated direction of the airbag cushion  100 , while the airbag cushion  100  is transversally inflated, the gas in the airbag cushion is induced to the center portion of the airbag cushion  100  along inclined directions of the divided lines  110   a  of the remaining first line portions  111 , and an unfolding speed of the airbag cushion  100  further increases. 
     As the airbag cushion  100  passes through the first line portions  111  that are closest to the inflator I and the second line portion  112 , while an initial unfolding speed of the airbag cushion  100  increases and a transversally inflated shape of the airbag cushion is maintained, the gas in the airbag cushion  100  is concentrated toward the center in the airbag cushion  100  by the divided lines  110   a  of the remaining first line portions  111 . As the gas partially flows toward the side ends of the airbag cushion  100 , an unfolding speed of the airbag cushion  100  increases and a fully unfolding shape of the airbag cushion  100  may be rapidly achieved. 
     The roof airbag for a vehicle with the above-described structure is configured such that the airbag cushion  100  is unfolded downward from the inner roof to protect the passenger seated on the seat, and the airbag cushion  100  is formed to be bent toward the passenger by the main tether  200  and the sub-tether  300 . Accordingly, a restraining force for the passenger is secured and the passenger can be safely protected from an impact. Furthermore, the airbag cushion  100  is efficiently unfolded by the sub-tether  300  without insertion between the roof-side portion of the vehicle body and the headlining. 
     Specifically, the transversal contraction of the airbag cushion  100  is prevented and the unfolding shape of the airbag cushion is maintained. Furthermore, the fluidity of the gas flow in the airbag cushion  100  is secured, and the airbag cushion  100  is rapidly unfolded. 
     Although the preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.