Abstract:
A cover for an air bag device in which a net body for reinforcement is buried characterized in that a bar-like body or a board-like body existing along the peripheral edge portion of said cover is buried in said cover and the edge portion of said net body completely covers the bar-like body or the board-like body.

Description:
FIELD OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a cover of an air bag device which protect an occupant of a vehicle in case of a collision of the vehicle, etc., and more particularly, to such a cover which is reinforced by a net body buried therein. 
     An air bag device has, as is known well, an air bag which is rapidly expanded in an emergency such as a collision of the vehicle. In a normal time, the air bag is folded and covered with a cover. The air bag is supported by an attaching board, for example, one named as a retainer. The cover is fixed to the attaching board by rivets, screws or bolts. 
     A cover of an air bag device of a type attached to a steering wheel of a vehicle is a bottomless, box-like cover with a lid having side wall portions and a canopy portion. Also, a cover with its side wall portions and a canopy portion reinforced by a net body is used. 
     The cover is provided with a line along which tearing begins (a tear line). The portion of the tear line is a portion of less strength compared with the surrounding portion and provided in a predetermined linear form. When the air bag is expanded, the cover is torn along the tear line. 
     When the cover is torn, considerably great tensile force acts on the cover. Therefore, a net body is buried in the cover to give necessary tensile strength to the portion of the cover except the tear line of the cover. 
     When the cover is torn, a great tensile load is added to the cover outwardly from the attaching board such as the retainer, and stress concentrates on through hole portions for attaching the cover for such as rivets, bolts, etc. Accordingly, a cover has been proposed in which a synthetic resin board is buried at the side wall portions and a net body is sewed on the synthetic resin board so that the tensile load may be dispersed all over the side wall portions (Japanese laid-open Utility application No. SHO 63-188257). 
     However, a cover with a synthetic resin board buried in its side wall portions has a problem that the side wall portions are difficult to be opened outward and to be deformed because of the high flexural rigidity of the side wall portions. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a cover of an air bag device which cover is firmly supported by a retainer, is not required to be excessively reinforced, and is deformed so as to be opened promptly when the air bag is expanded. When the cover is torn, force is dispersed over a bar-like body or a board-like body. 
     A cover of an air bag apparatus of the present invention is characterized in that a bar-like body or a board-like body is buried in the cover along the peripheral edge portion of the cover and a net body completely covers the bar-like body or the board-like body. 
     A cover of the present invention is fixed to an attaching board such as a retainer by, for example, rivets, bolts, or screws (hereinafter also referred to as rivets, etc.). As a bar-like body or a board like body is buried along the peripheral edge of the cover, the rivets, etc. directly pierce the bar-like body or the board-like body, or, pierce the center side of portions, for example, a canopy portion rather than the bar-like body or the board-like body. Consequently, when force in the direction away from the attaching board is given to the cover in expanding, the force is first given to the net body, and then, is dispersed over the bar-like body or the board-like body connected with the net body. Accordingly, even when the cover is expanded, the cover is supported firmly by the attaching board such as a retainer. In addition, the bar-like body or the board-like body does not exist at the portion of the cover which is opened and deformed when the cover is expanded, and thus the cover is deformed so as to be opened promptly to the side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a cover of an air bag device of an embodiment of the present invention; 
     FIGS. 2 and 3 are partial sectional views of the cover; 
     FIG. 4 is a sectional view of the cover when expanded; 
     FIGS. 5, 6 and 7 are sectional views showing other embodiments; and 
     FIG. 8 is a perspective view showing an engagement of a net body and a bar-like body. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view of a cover of an air bag device of an embodiment of the present invention. FIGS. 2 and 3 are sectional views taken along the line II--II and the line III--III, respectively, of FIG. 1. FIG. 4 is an explanatory view of deformation of the cover when expanded. 
     A cover 10 of the air bag device relates to a cover of an air bag device which is attached to a steering wheel. The cover 10 is a bottomless box-like shape with a lid and is provided with side wall portions 12 and canopy portion 14. A net body 16 for reinforcement is buried at the side wall portions 12 and the canopy portion 14. A bar-like body 18 is buried at the side wall portions 12 of the cover 10 so as to be extended along the peripheral edge portions of the side wall portion 12. The edge portions of the net body completely cover the bar-like body. 
     In the present embodiment, the edge portions of the net body (a net-like body made of synthetic fiber of high strength or metal) 16 returned up so as to wrap the bar-like body 18. The free-end side 16a which is turned up and the base-end side 16b of the net body 16 are combined with each other by sewing or adhering. Characters A and B designate the combined portions. In the present invention, the combined portion B is located adjacent to the bar-like body 18 and the combined portion A is located adjacent to the free end of the net body. Through holes 22 are bored for rivets, etc. 20 at the combined portions A and B. The side wall portion 12 overlaps side board portion 24a of a retainer 24 and is fixed by the rivets, etc. 20. An air bag 30 and an inflater 32 are attached to the retainer 24. 34 designates a ring for fixing the air bag 30. 
     In an air bag device comprising the cover 10 of the air bag device structured as abovementioned, when the air bag is expanded by gas blown off from the inflater, the cover 10 is torn along tear lines 26 of the canopy portion 14 as shown in FIG. 1. Further, as shown in alternate long and two short dashes lines of FIG. 4, the side wall portion 12 is opened and deformed so as to warp outward. When the cover is torn like this, force F in the direction away from the retainer 24 is given to the cover 10. The force F in the direction away from the container is dispersed all over the side wall portion 12 through the bar-like body 18. Particularly, in the present embodiment, the bar like body 18 is caught in rivets, etc. 20. Accordingly, even the great tensile force F is given to the cover 10, the side wall portion 12 of the cover 10 are firmly supported by the retainer 24. In addition, the bar-like body 18 does not exist at upper portion of the side wall portions 12 which are opened and deformed when the cover is torn (portions on the side of an occupant in respect to a board of the retainer 24) and thus the cover 10 is deformed so as to be opened promptly to the side. 
     FIGS. 5 and 6 show other embodiments of the present invention and show structures of the same sectional portion as shown in FIGS. 2 and 3. 
     In the present embodiment, a board-like body 28 instead of the bar-like body 18 is buried. A through hole 22 for rivets etc. is bored so as to pierce the board-like body 28. 
     FIG. 7 is a sectional view showing still another embodiment of the present embodiment (showing the same sectional portion as shown in FIGS. 2 and 3). FIG. 8 is a perspective view for explaining a state of engagement of the bar-like body 18 and the net body 16. 
     In the present embodiment, the bar-like body 18 is wrapped by the peripheral edge portion of the net body 16 by passing through meshes of the peripheral edge portion of the net body 16 from one side to the other side. 
     The through hole 22 for rivets, etc. is bored on the side of the canopy portion 14 in respect to the bar-like body 18. 
     In the embodiments shown in FIGS. 5 through 8 also, when the cover is torn, the side wall portions 12 are firmly supported by the retainer, and in addition, the cover 10 is deformed so as to be opened promptly to the side. 
     The embodiments as abovementioned relate to a cover of an air bag device which is attached to a steering wheel. The present invention, however, can be applied also to other types of an air bag device, such as an air bag device which is provided at an instrumental panel.