Abstract:
An airbag device having an airbag that can be inflated and deployed by inflating gas; a gas generator that supplies the inflating gas to the inside of the airbag; a housing that accommodates the airbag in a folded state; and a cloth-like deployment restricting member that is fixed at one end to the housing and that encloses part of the folded airbag. A deployment non-restricted portion of the airbag deploys upward, the deployment non-restricted portion not being enclosed by the deployment restricting member, and a deployment restricted portion, which is enclosed by the deployment restricting member, is deployed afterward.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an airbag device for installation on a vehicle. In particular, the present invention relates to an airbag device suitable for the so-called knee airbag aimed at protection of occupant&#39;s lower leg regions. 
     2. Related Technology 
     Vehicles such as automobiles are provided with an airbag system in which a bag is rapidly inflated by gas to prevent the occupants from colliding with dangerous zones, thereby minimizing or preventing injuries or death occurring when the occupant hits a hard part inside the vehicle, such as a steering wheel of front glass, during collision. 
     When the vehicle collides, the occupant is moved forward by the inertia force and the occupant&#39;s knees strike against the instrument panel. In order to protect the occupant from such an impact, an airbag device that inflates from the lower surface of the instrument panel has been suggested. 
     It is desirable that an airbag device could safely restrain the occupant even in cases with different sitting postures of the occupant (for example, a posture close to the instrument panel). However, according to the invention described in Japanese Patent Application Publication No. 10-315894, when the occupant is abnormally close to the instrument panel, the airbag may cause significant damage to the occupant. 
     SUMMARY OF THE INVENTION 
     The present invention has been created with the foregoing in mind, and it is an object thereof to provide an airbag device that can reduce, while having a simple structure, the possible damage to the occupant caused by a deployed airbag. 
     The airbag device in accordance with the present invention includes: an airbag that protects, by inflation and deployment thereof, lower leg regions of an occupant; a gas generator that supplies an inflating gas to the inside of the airbag; a housing that accommodates the airbag in a folded state; and a cloth-like deployment restricting member that is fixed at one end thereof to the housing and encloses part of the folded airbag. The airbag initially deploys upward from a deployment non-restricted portion, which is not enclosed by the deployment restricting member, with a deployment restricted portion, which is enclosed by the deployment restricting member, being deployed afterward. The non-restricted portion is provided at a position corresponding to the vicinity of the lower portion of the occupant&#39;s kneecaps when the airbag has deployed. 
     According to the present invention having the above-described configuration, the deployment direction and deployment speed of the airbag can be controlled by the deployment restricting member, and potential injury to the occupant by the deployed airbag can be reduced. In particular, in a knee airbag device, a pressure applied close to the occupant&#39;s knees can be dispersed by initially deploying the upper portion of the airbag and then deploying, with a delay, the lower portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory drawing illustrating the operation of a conventional knee airbag. 
         FIG. 2  is an exploded perspective view of a knee airbag device according to a first embodiment of the present invention. 
         FIG. 3(A)  is an elevational view illustrating the structure of the knee airbag device according to the first embodiment.  FIG. 3(B)  is the cross-sectional view generally along line A-A shown in  FIG. 3(A) . 
         FIGS. 4(A) and 4(B)  are views illustrating the process of assembling the knee airbag device according to the first embodiment. 
         FIG. 5  is an explanatory drawing illustrating the arrangement of the knee airbag device according to the first embodiment. 
         FIGS. 6(A)  and (B) illustrates the operation of the knee airbag device in accordance with the present invention. 
         FIG. 7(A)  is an elevational view illustrating the structure of a knee airbag device according to a second embodiment of the present invention and  FIG. 7(B)  is a view illustrating the structure of the deployment restricting member used therein. 
         FIGS. 8(A) and 8(B)  are an elevational view illustrating the structure of a knee airbag device according to a third embodiment of the present invention and a plan view illustrating the structure of the deployment restricting member used therein. 
         FIG. 9  is a graph illustrating the effect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is an explanatory drawing illustrating the operation of the conventional knee airbag. In  FIG. 1 , an airbag device  10  is accommodated on the inner side of an instrument panel  12 . An airbag  16  is accommodated in a folded state inside a housing  14  and configured to inflate and deploy toward the outside when the device is actuated. 
     In the knee airbag device of such a structure, a large pressure is concentrated in a leg portion “L” (in particular, kneecap portion) of the occupant at the initial stage of deployment of the airbag  16  and, therefore, potential for injury to the occupant is great. This problem is particularly severe in the case in which the occupant gets abnormally close to the instrument panel  12 . 
       FIG. 2  is an exploded perspective view of a knee airbag device  110  according to a first embodiment of the present invention.  FIG. 3(A)  is a top view illustrating the structure of the knee airbag device  110  according to the first embodiment.  FIG. 3(B)  is the cross-sectional view in the A-A direction shown in  FIG. 3(A) . The knee airbag device  110  according to the present embodiment can be installed, for example, in part of the glove box lid. 
     The knee airbag device  110  includes an airbag  116  that protects leg regions of the occupant by inflation and deployment when the device is actuated; an inflator  112  that supplies an inflating gas to the airbag  116 ; a housing  114  that is fixed to the vehicle and accommodates the airbag  116  in a folded state; and a deployment restricting member  118  that restricts the deployment of the airbag  116  inside the housing  114 . 
     The housing  114  is molded in quadrangular box shape and the upper side thereof is open. As described below, the airbag  116  is accommodated inside the housing  114  in a state in which the airbag is folded in the up-down direction and then wound in a roll shape from both the left and right sides toward the center. 
     The restricting member  118  can be formed, for example, from a material similar to that of the airbag  116 . As shown in  FIG. 2 , the restricting member  118  is shaped in a long thin band and has formed therein two holes for inserting attachment bolts provided at the inflator  112 . In the present embodiment, the restricting member  118  is fixed to the housing by the attachment bolts, but the restricting member  118  may be also directly attached by stitching or adhesive bonding to the airbag fixed to the housing. 
     As shown in  FIG. 3 , the restricting member  118  is configured to enclose a lower portion of the front surface, a lower portion of the side surface, and part of the bottom surface of the folded airbag  116 . The restricting member is attached so that the surface shown in  FIG. 3(A)  faces from the instrument panel toward the inside of the vehicle. 
       FIGS. 4(A) and 4(B)  are views illustrating the process of assembling the knee airbag device  110  according to the first embodiment. The airbag  116  according to the present embodiment is initially wound or folded toward the center of the airbag  116  in the up-down direction (or front-rear direction), as shown in  FIG. 4(A) . Then, as shown in  FIG. 4(B) , the airbag is wound from the left and right or lateral ends toward the center of the airbag  116 . In this case, when the airbag  116  accommodated inside the housing  114  is wound from the left and right sides, the airbag is not completely wound through the central portion. Rather, and the central portion is kept in an unwound state. 
     The lower portion of the folded airbag  116  is then enclosed with the restricting member  118 . The state of the enclosed airbag  116  is shown in  FIG. 3 . When the airbag  116  is enclosed with the restricting member  118 , one end of the restricting member  118  is fixed to the housing  114  and in this state the band-like portion of the restricting member  118  is folded toward the upper portion of the airbag  116  so as to cover the lower portion of the front surface of the airbag  116 . 
     Both ends of the band-like portion of the restricting member  118  are inserted so as to be wrapped around the side surface toward the bottom or back surface of the airbag  116 . In this case, as shown in  FIG. 3(B) , it is preferred that the end portions of the restricting member  118  be apart from each other, rather than in contact with each other, along the bottom surface of the airbag  116 . The dimension D of the enwrapping portion of the restricting member  118  can be, for example, from 20 mm to about 70 mm. With such a configuration, no unnecessary restriction is placed on the deployment of the airbag  116 . As a result, rapid deployment can be performed. 
       FIG. 5  is an explanatory drawing illustrating the arrangement of the knee airbag device  110  according to the first embodiment and in relation to an occupant&#39;s lower leg portion L. In the present embodiment, the height H 1  from a vehicle floor surface  100 F should be set optimally so that the upper end portion or limit of the restricting member  118  is positioned close to the lower portions of kneecaps of the adult occupant in an irregular seating position. In the figure, the deployment non-restricted region (upper half) of the airbag  116  is encircled by the dotted line denoted by  116   a  and the deployment restricted region (lower half) is encircled by the dotted line denoted by  116   b.    
     In the present embodiment, the deployment restriction of the airbag with the above-described restricting member  118  and the arrangement such as shown in  FIG. 5  make it possible to reduce the application of excess pressure to the occupant. 
       FIG. 6(A)  shows a state in which a lower leg portion L of the occupant is generally in contact with the instrument panel  12 . Where the airbag device  110  is actuated by front collision of the vehicle, or the like, the inflating gas is supplied from the inflator  112  into the airbag  116 . The inflating gas starts the deployment of the airbag  116 , but initially the upper portion, the deployment non-restricted region  116   a , of the airbag  116  is deployed upward, as shown in  FIG. 6(B) , due to the action of the restricting member  118 . Then, the lower portion, the deployment restricted region  116   b , is deployed. Therefore, the deployed shape of the airbag  116  is long in the up-down direction and local application of a large pressure to the occupant can be avoided. 
       FIGS. 7(A) and 7(B)  are an elevational view illustrating the structure of the knee airbag device according to the second embodiment of the present invention and a plan view illustrating the structure of the deployment restricting member  218  used therein. The knee airbag device according to the present embodiment differs from the knee airbag device  110  according to the above-described first embodiment in the shape of the deployment restricting member. Other constituent elements are the same and redundant explanation thereof is therefore omitted. 
     The deployment restricting member  218  according to the present embodiment is provided with a base portion  234  that is fixed to a housing  214 , a recess  232  forming a deployment non-restricted region of an airbag  216 , and left and right side portions  236  covering the side surfaces of the airbag  216 . In the present embodiment, the entire roll portions positioned on the left and right sides of the folded airbag  216  are enclosed by the restricting member  218 , while an upper center portion of the airbag  216  is not enclosed as a result of the recess  232 . Where such a configuration is used, only the upper portion of the airbag  216  is initially deployed and thereafter the side and lower portions are deployed. Thus, in the present embodiment, the airbag  216  is preferentially deployed from the top portion in the center thereof. 
       FIGS. 8(A) and 8(B)  are an elevational view illustrating the structure of the knee airbag device according to the third embodiment of the present invention and a plan view illustrating the structure of the deployment restricting member  318  used therein. The knee airbag device according to the present embodiment differs from the knee airbag devices according to the above-described first and second embodiments in the shape of the deployment restricting member  318 . Other constituent elements are the same and redundant explanation thereof is therefore omitted. 
     The deployment restricting member  318  according to the present embodiment is provided with a base portion  334  that is fixed to a housing  314 , a recess  332  forming a deployment non-restricted region of an airbag  316 , and left and right side portions  336  covering the side surface of the airbag  316 . The restricting member  318  is further provided with extension regions  338 , between the recess  332  and the left and right side portions  336 , that extend transverse to the side portions  336  and that are to be locked to hooks  314   a  of the housing  314 . In the present embodiment, similarly to the above-described second embodiment, the roll portions positioned on the left and right sides of the folded airbag  316  are entirely enclosed by the side portions  336  and extension regions  338  of the deployment restricting member  318 . 
     Locking holes  340  are formed at distal ends of the extension regions  338  of the restricting member  318 , and these locking holes  340  engage with the hooks  314   a  of the housing  314 . The locking holes  340  are provided so that they can be easily fractured when the airbag  316  is deployed. 
     Where the airbag device according to the present embodiment is actuated, only the center of the upper portion of the airbag  316  is initially deployed through the area defined by the recess  332 , and thereafter the locking holes  340  are fractured and the restricted side portions and lower portion are deployed. Thus, in the present embodiment, the deployment of the airbag from the central upper portion can be said to be even more preferential than in the second embodiment. 
     The embodiments of the present invention are described above, but the present invention is not limited to the abovementioned embodiments and various design changes can be made without departing from the technical concept of the invention described in the claims.