Abstract:
An air bag consists of a front panel and rear panel. An inflater mounting opening is provided at the central portion of the rear panel. The rear panel and the front panel are connected to each other at a vicinity of the center thereof by threads. The threads allow the air bag to extend sideward at first, and then the threads are chopped so as to allow the air bag to extend forward.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an air bag and an air bag device for extending an air bag at the time of a collision of a vehicle to protect an occupant and particularly, to an air bag and an air bag device to be mounted in a steering unit and suited as an air bag device for a driver. More particularly, the present invention relates to an air bag device which is improved to have the air bag quickly extended vertically and horizontally. 
     2. Description of the Related Art 
     The air bag device to be mounted in a stationary portion in front of a seat of a vehicle is intended to protect an occupant in an emergency such as a collision, by inflating (or extending) the air bag with pressure of gas injected from a gas generator called an &#34;inflater&#34;. 
     FIG. 10 shows an example of an air bag device for a driver of the prior art. An inflater 14 has a leading end fitted in a central opening (or inflater mounting hole) 12 which is formed in a main plate 10a of a retainer 10. 
     An air bag 16 is formed with a receiving hole 18 for receiving a leading end of the inflater 14. The receiving hole 18 is arranged around a peripheral edge of the mounting hole 12. The receiving hole 18 of the air bag has a peripheral edge held on the peripheral edge of the mounting hole 12 by a holding ring (or patch) 20. 
     The air bag 16 and the inflater 14 are fixed on the retainer 10 by fixing stud bolts 38 on the holding ring 20, by threading the stud bolts 38 into bolt holes of the air bag 16, bolt holes of the retainer 10 and bolt holes formed in a flange of the inflater 14, and by fastening nuts 40. 
     The air bag 16 is folded in an extensible state and covered with a module cover 22. The module cover 22 is torn by pressure of inflation of the air bag 16 when the air bag 16 is extended by gas injected from the inflater 14. 
     The driver&#39;s air bag device is desirable to protect the driver by extending the air bag 16 quickly at first in the vertical and horizontal directions in front of the driver when the inflater 14 is activated. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an air bag and an air bag device which has an air bag quickly extended vertically and horizontally in front of a driver when an inflater is activated. 
     According to an air bag of a first aspect, the air bag has an opening for an inflater in a central portion of a rear panel thereof. A central portion of a rear panel of the air bag is connected to a front panel of the air bag by means of a connecting mechanism. The mechanism allows the air bag to extend forward after at least a part thereof extends sideward completely. 
     According to an air bag of a second aspect, the connecting mechanism of the first aspect consists of adhesion by adhesive. 
     An air bag device of the present invention has a retainer having a main plate, an inflater mounting opening formed in a central portion of the main plate, an inflater having a leading edge mounted in the opening of the retainer and having a plurality of gas injection ports in its side periphery, an air bag mounted on the retainer and being folded in an expandable shape by an injection of gas from the inflater, a module cover covering the air bag capable of being torn when the air bag expands. The air bag is folded in a first direction which extends along the main plate of the retainer, then folded in a second direction which crosses perpendicularly the first direction. The rear panel and the front panel of the air bag are sewn together by a thread. Stitches of the thread extends straight along a folding line made by a first folding in the first direction. The thread of the stitches is chopped after the air bag is extended in the second direction. As a result, the air bag extends sideward in the second direction at first, and then the air bag extends sideward in the first direction and also forward. 
     Connecting strength between the rear panel and the front panel can be set as desired by predeterming the tensile strength of the thread and also by selecting the number of the stitches for the seam. 
     According to the air bag of the present invention, since the central portion of the rear panel and the front panel are connected, the gas injected from the inflater extends the air bag sidewardly in a radial direction. When the air bag makes a sideward extention of at least a part thereof, injected gas pressure tends to apply mainly to the direction which makes the front panel and the rear panel separate. Thereby, the air bag extends forward. 
     According to the second aspect, the adhesion by adhesive causes the front panel and the rear panel of the air bag to be easily connected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a plan view of an air bag 50 according to the present invention. 
     FIG. 1B is a side view of the air bag 50 taken along a line 1B--1B in FIG. 1 according to the present invention. 
     FIG. 2A is a plan view of the air bag 50 being folded. 
     FIG. 2B is a side view of the air bag 50 taken along a line 2B--2B in FIG. 2A. 
     FIG. 3A is a plan view of the air bag 50 being folded. 
     FIG. 3B is a side view of the air bag 50 taken along a line 3B--3B in FIG. 3A. 
     FIG. 4A is a plan view of the air bag 50 being folded. 
     FIG. 4B is a side view of the air bag 50 taken along a line 4B--4B in FIG. 4A. 
     FIG. 5A is a plan view of the air bag 50 being folded. 
     FIG. 5B is a side view of the air bag 50 taken along a line 5B--5B in FIG. 5A. 
     FIG. 6A is a plan view of the air bag 50 being folded. 
     FIG. 6B is a side view of the air bag 50 taken along a line 6B--6B in FIG. 6A. 
     FIG. 7 is a sectional view taken along the line 7--7 of FIG. 1. 
     FIG. 8 is a sectional view showing an inflater 46. 
     FIG. 9 is a longitudinal sectional view of an air bag device according to an embodiment. 
     FIG. 10 is a longitudinal sectional view showing the air bag device of the prior art. 
     FIG. 11 is a plan view of the air bag 50A according to another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described in the following with reference to the accompanying drawings. 
     As shown in FIG. 9, an air bag device of the embodiment is constructed by attaching both an inflater 46 and an air bag 50 to be extended by the inflater 46 to a main plate 44a of a retainer 44 and by covering the folded air bag 50 with a module cover 48. 
     The air bag 50 consists of a front panel 50a and a rear panel 50b. The panels 50a, 50b are overlapped and sewn at their peripheral portion together by a sewing machine to form the air bag. 
     This air bag 50 takes a flattened disc shape, as shown in FIGS. 1A and 7, when it is not supplied with the gas. The bag 50 has at the center of the rear panel 50b an opening 52 for receiving the leading end of the inflater 46. The air bag 50 has vent holes 54 for inhaling the air, when it is extended, and for releasing the gas from its inside, after extended, to absorb the shocks coming from the human body hitting the air bag 50. 
     The front panel 50a and the rear panel 50b of the air bag 50 are sewed at two seams 56, 58 extending parallel to the direction of the diameter of the air bag 50. 
     The method of folding the air bag 50 will be described in the following with reference to FIGS. 1A to 6B. At first, as shown in FIG. 2, the air bag 50 has its lefthand half folded to the front along a fold 61 slightly offset to the left from the center. As shown in FIGS. 3A and 3B, the folded half has its leading end folded back along a fold 62 extending in parallel with the fold 61. Then, as shown in FIGS. 4A and 4B, the remaining righthand half of the air bag 50 is folded back along a fold 63 which is slightly offset to the right from the center but in parallel with the fold 62, and the folded leading end is further folded back along a fold 64 which is also in parallel with the fold 63. 
     In these ways, the air bag 50 is folded several times in a first direction 1 into a rectangular shape, as shown in FIG. 5A. After this, the rectangular air bag 50 is folded back in a zigzag manner along folds 65, 66 and 67 until it takes a generally square shape as shown in FIGS. 6A and 6B. 
     The air bag 50 thus folded is then covered with the module cover 48 so that the air bag device shown in FIG. 9 is prepared. 
     As shown in FIG. 8, the inflater 46 has its inside divided by four radially extending partitions 70, 72, 74 and 76 into four compartments 78, 80, 82 and 84. These compartments 78 to 84 are individually charged with gas generating agents. The inflater 46 is equipped at its center with an igniter 86, which is disposed to face the compartments 78 and 82 only. The partitions 70 to 76 are individually formed with openings 88 for allowing the gas produced by the reactions of the agents in the compartments 78 and 82 to be partially injected therethrough into the compartments 80 and 84 to cause the gas producing reactions of the agents in the compartments 80 and 84. Incidentally, the individual compartments 78 to 84 are formed with keyhole openings 90 for allowing the inside gases to flow therethrough into the air bag 50. These openings 90 are equipped along their inner faces with (not-shown) particulate trapping members made of mesh. 
     In the air bag device thus constructed, the gas is injected at first in a second direction 2 when the inflater 46 is activated. After lapse of a predetermined time, the gas is injected in the first direction 1. As a result, the air bag is unfolded or extended in the order of FIGS. 6, 5, 4, 3, 2 and 1. 
     In this instance, the gas is injected at first in the second direction so that the air bag 50 is extended in the second direction. This second direction 2 is aligned with the direction, in which the gas is injected from the inflater 46, as shown in FIGS. 5, 6 and 8, so that the injected gas pressure is substantially effective to function to extend the air bag 50 vertically of FIG. 5A. 
     After the air bag 50 is extended in the second direction shown in FIG. 5A, the injected gas pressure from the inflater is applied to the air bag 50 to widen thereof in the first direction and to extend forward. The air bag 50 extends in the first direction and forward when the thread constituting the seams 56, 58 is chopped. In this case, the thread strength and the number of the stitches are preferably selected such that the thread of the seams 56, 58 is chopped after the air bag 50 extends in the first direction. 
     As described above, according to the air bag device of the embodiment, the air bag extends quickly in the direction along the main plate of the retainer 44 (up and down or right and left direction for the occupant of the driver&#39;s seat). Thereafter, the air bag extends in the direction towards the occupant. 
     In the embodiment described above, the front panel 50a and the rear panel 50b are connected by the seams 56, 58 stitched by a thread. However, the panels 50a and 50b may be bonded by an adhesive. 
     In the embodiment described above, the panels 50a, 50b are connected by the straight seams 56, 58. However the panels 50a, 50b may be connected by threads as an adhesive at plural points around the inflater inserting opening 52 as shown in FIG. 11. In FIG. 11, the panels are connected at four points of 59a, 59b, 59c and 59d. 
     As has been described hereinbefore, according to the present invention, the air bag can be quickly extended vertically and horizontally. Moreover, the injected gas pressure of the inflater effectively acts as the force to extend the air bag so that the air bag can be quickly extended even with a reduced inflater capacity.