Air bag inflator having circumferentially disposed auto ignition material

An inflator of an air bag device includes a cylindrical vessel having gas releasing openings disposed at the circumferential surface thereof, a gas generating agent disposed in the vessel, a boosting agent for starting a gas generating reaction of the gas generating agent, and an igniting agent having an ignition point lower than that of the boosting agent. The igniting agent is disposed over almost the entire inner surface of the vessel.

FIELD OF THE INVENTION 
The present invention relates to an inflator of an air bag device for use 
in a passenger seat. 
DESCRIPTION OF THE RELATED ART 
An inflator of an air bag device for use in a passenger seat comprises a 
cylindrical vessel having gas releasing openings disposed at the 
circumferential surface, a gas generating agent charged in the vessel, a 
boosting agent for initiating a gas generating reaction of the gas 
generating agent and an igniting agent having an ignition point lower than 
that of the boosting agent. The vessel is usually made of aluminum or 
aluminum alloy. 
As described in Japanese Patent Laid Open Hei 2-63951 corresponding to U.S. 
patent application Ser. No. 190,479 (filed on May 4, 1989) and Japanese 
Patent Laid Open Hei 2-74441 corresponding to German Patent Application 
DEP 3824469.1 (filed on Jul. 19, 1988), an igniting agent is disposed so 
as to react the gas generating agent before the strength of the aluminum 
or aluminum alloy is reduced to the point of failure when the inflator of 
the air bag device encounters a fire accident and the peripheral 
temperature thereof is elevated. Since the ignition point (reaction 
starting temperature) of the igniting agent is lower than that of the 
boosting agent, the igniting agent ignites first upon a fire to ignite the 
boosting agent by the heat and, as a result, the gas generating agent 
starts the gas generating reaction. 
Upon collision of a vehicle, an electric igniting device disposed 
separately ignites the boosting agent. 
The igniting agent has been disposed to a portion at one end face of the 
vessel as shown in FIG. 2 of Japanese Patent Laid Open Hei 2-63951 and 
FIG. 1 of Japanese Patent Laid Open Hei 2-74441. 
In the inflator of the air bag device in which the igniting agent is 
disposed to one end face of the vessel, when the inflator undergoes heat 
of fire from the other end thereof, ignition of the igniting agent is 
delayed by the period of time that the heat conducts from the other end to 
the one end. 
OBJECT AND SUMMARY OF THE INVENTION 
An object of the present invention is to provide an inflator in which an 
igniting agent ignites in an early stage in response to fire when the 
inflator is exposed to a fire and any part of the inflator is heated. 
An inflator of an air bag device in the first aspect of the present 
invention comprises a cylindrical vessel having gas releasing openings 
disposed at the circumferential surface, a gas generating agent charged in 
the vessel, a boosting agent for starting the gas generating reaction of 
the gas generating agent and an igniting agent having an ignition point 
lower than that of the boosting agent, wherein the igniting agent is 
disposed so as to be distributed over almost the entire inner surface of 
the vessel. 
In the second aspect of the present invention, in an inflator of an air bag 
device as defined in the first aspect, the igniting agent is deposited 
substantially over the entire inner surface of the vessel. 
In the inflator of the air bag device in accordance with the present 
invention, since the igniting agent is applied to the wide range of the 
inner surface of the vessel, the igniting agent ignites in an early stage 
when any part of the inflator is heated on a fire.

PREFERRED EMBODIMENT 
Description will now be made to preferred embodiments of the present 
invention with reference to the drawings. 
A vessel 1 is in a cylindrical shape and has a plurality of openings 2 
perforated at the circumferential portion thereof. The vessel 1 is made of 
aluminum or aluminum alloy. An igniting agent 3 is coated over the entire 
inner surface of the vessel 1. A boosting agent 4 is disposed along the 
axial center of the vessel 1. A gas generating agent is disposed around 
the boosting agent 4. 
A filter 7 is disposed along the inner circumferential surface of the 
vessel 1 coated with the igniting agent 3. The filter 7 has a function of 
filtering a gas jetting out through the openings 2. An electric igniting 
device 8 is disposed at one end face of the vessel 1. The electric 
igniting device 8 has a wire that generates heat upon electric current 
supply and a gunpowder, in which the gunpowder is ignited upon electric 
current supply to the wire, so that the boosting agent 4 ignites and the 
gas generating agent 5 starts reaction. 
In the air bag device having the inflator having thus been constituted, 
when a vehicle having the air bag device mounted thereon is involved in an 
accident such as collision of a vehicle, electric current is supplied to 
the electric igniting device 8, in which the boosting agent 4 ignites and 
the gas generating agent 5 starts reaction as described above to rapidly 
generate a great amount of gases. The gases are jetted out through the 
openings 2 to extend the air bag rapidly. 
When the inflator is exposed to a fire, the igniting agent 3 ignites first 
and, successively, the boosting agent 4 and the gas generating agent 5 
also starts reaction. Generated gases are released through the openings 2. 
In this inflator, since the igniting agent 3 is disposed over the entire 
inner surface of the vessel 1, the igniting agent 3 ignites at an early 
stage when any part of the inflator is heated by a fire, so that gas is 
generated from the inflator while the vessel 1 maintains a sufficient 
strength. Accordingly, the vessel 1 is free from bursting. 
In this embodiment, since the igniting agent 3 is coated on the inner 
surface of the vessel 1, the igniting agent 3 can easily be deposited 
uniformly over the entire inner surface of the vessel 1. 
In this embodiment, the igniting agent 3 is deposited over the entire inner 
surface of the vessel 1 but, instead, the igniting agent 3 may be applied 
over the entire inner surface of the vessel 1 in a scattered pattern or 
intermittently as shown in FIG. 2. Alternatively, the igniting agent 3 may 
be applied in a striped pattern over the entire inner surface of the vessel 
1 as shown in FIG. 3. 
Further, the igniting agent 3 is coated also to both end faces of the 
vessel 1 in this embodiment, but the igniting agent may be applied only to 
the inner circumferential surface of the vessel 1. 
In the present invention, BKNO.sub.3 (boron potassium nitrate) mixed with 
TiH.sub.2 (hydrogenated titanium) and KClO.sub.4 (potassium perchrolate) 
may be used, for example, as the boosting agent. Smokeless powder that 
ignites at about 150.degree. C.-200.degree. C. is suitable for instance as 
the igniting agent. 
As has been described above, with the inflator according to the present 
invention, since the igniting agent ignites at an early stage irrespective 
of the direction of heat applied to the inflator upon a fire accident, the 
gas generating reaction of the gas generating agent proceeds while the 
vessel still maintains a sufficient strength.