Compressed gas storage means for a vehicle occupant restraining system

A compressed gas storage means for a vehicle occupant restraining system comprising a storage container having a chamber formed therein, the chamber containing gas stored under a high pressure and having an internal wall surface bearing a coating of a material with a high specific surface area.

FIELD OF THE INVENTION 
The invention relates to a compressed gas storage means for a vehicle 
occupant restraining system comprising a storage container having a 
chamber containing gas stored under high pressure. 
BACKGROUND ART 
Compressed gas storage means, more especially for the inflation of a gas 
bag for a vehicle occupant restraining system, are opened in a crash by 
activation of small pyrotechnic charge so that the gas stored in the 
storage container may escape and cause deployment of the gas bag. In this 
respect the gas bag must completely deploy within an extremely short 
period of time, a high gas pressure being required for rapid filling of 
the gas bag and such gas pressure must be maintained in the final phase of 
deployment as well. A gas pressure which is only high at the outset on the 
contrary tends to be an obstacle for the initial part of deployment and is 
unable to ensure full deployment of the gas bag. 
SUMMARY OF THE INVENTION 
The invention is to provide a compressed gas storage means, in the case of 
which, without any change in volume, a larger amount of gas may be stored 
so that in the final phase of the deployment operation there is still 
sufficient gas for complete deployment of the gas bag. In the case of a 
compressed gas storage means of the type initially mentioned this is 
rendered possible by the invention because the inner wall surface of the 
chamber bears a coating of a material with a high specific surface area. 
Preferably, the material possesses a specific surface area within a range 
of 200 to 400 m.sup.2 /g. In a particularly preferred embodiment of the 
invention the said material is an oxide or a molecular sieve and, most 
preferred, a zeolite. 
Further features and advantages of the invention will be apparent from the 
following description of a preferred embodiment and from the following 
drawings, to which reference is had.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 a compressed gas storage means is shown, which serves for the 
inflation of a gas bag, not illustrated, as part of a complete gas bag 
module. In the interior of the storage container 1 there is a chamber 3 
charged with an inert gas such as for example argon or helium, or with 
air. However, it would be possible to employ other gases or gas mixtures 
utilized in industry. The gas stored in the chamber 3 is under a pressure 
of over 200 bar. A charging end 5 positioned at the front face is located 
opposite to a discharge end 7. From the discharge end an ignition unit 9 
extends into the interior of the chamber 3. The ignition unit 9 comprises 
a pyrotechnic charge which in a crash is fired in response to a signal. 
The end wall 11 at the discharge end 7 possesses a plurality of discharge 
openings 13 distributed evenly about a periphery, such openings being 
separated in the non-operated state of the unit by a wall 15 from the 
chamber 3. On a connection pin 17, extending out from the end wall 11, of 
the ignition unit 9 a diffusor baffle 19 is mounted which has numerous 
discharge openings 21. This baffle 19 of the storage container 1 extends 
into the interior of a gas bag, not illustrated, with the storage 
container and the gas bag forming a gas bag module. 
The interior wall surface of the chamber 3 bears a coating 23 of a material 
with a high specific surface area, preferably a zeolite, the specific 
surface area of the material preferably being within a range of 200 to 400 
m.sup.2 /g. As a material with a high specific surface area other oxides 
or molecular sieves may also be employed. The specific surface area of the 
material may also be larger than 400 m.sup.2 /g. 
The manner of operation of the compressed gas storage means of the 
invention will be explained in the following: 
Owing to the adhesion or adsorption forces acting on the gas molecules the 
coating 23 applied to the inner wall surface of the chamber 3 renders it 
possible for there to be a compaction of the gas introduced into the 
chamber on the surface of the coating until a liquid condition is 
attained. Accordingly, for the identical volume of the chamber 3 it is 
possible for a larger quantity of gas to be stored. In a crash the 
pyrotechnic charge located in the ignition unit 9 will be fired so that 
additional gas will flow into the interior of the chamber 3. The pressure 
in the chamber 3 is consequently so increased that the wall 15 will 
rupture and gas will flow through the discharge openings 13 through the 
diffusor baffle 19 and via the discharge openings 21 into the interior of 
the gas bag. With the reduction in the internal pressure the coating 23 
will release the gas adsorbed on its surface so that in the final phase of 
the deployment operation such additional gas will be made available for 
complete deployment of the gas bag. 
FIG. 2 diagrammatically shows the variation in pressure within the chamber 
3 as a function of time (t). As described above, the internal pressure in 
the chamber will rise immediately following activation of the pyrotechnic 
charge in order, after rupture of the wall 15, to fall again sharply. In 
the case of a compressed gas storage means without a coating the drop in 
pressure is sharper or steeper than in the case of compressed gas storage 
means of the invention and the internal pressure in the chamber approaches 
the pressure of the surroundings more rapidly. In the final phase of 
deployment of the gas bag the internal pressure in the chamber of the 
compressed gas storage means of the invention is hence higher than in 
compressed gas storage means known so far. 
Much the same applies for the variation with time of the mass flow from the 
chamber 3 as represented diagrammatically in FIG. 3. The release of the 
pyrotechnic charge firstly leads to a rise in the quantity of gas inside 
the chamber 3. After the rupture of the wall 15 the gas flows into the gas 
bag and causes the deployment thereof. However, owing to the adsorption of 
gas on the coating 23 the liberation of gas is delayed in time so that the 
final phase of the deployment operation a larger quantity of gas is made 
available than in the case of customary compressed gas storage means. 
Moreover, with the use of the compressed gas storage means of the invention 
there is a smaller effect of the ambient temperature on the deployment 
operation, since the coating 23 functions as an accumulator and variations 
in temperature are more readily compensated for. 
For the production of the compressed gas storage means of the invention the 
chamber 3 is treated with a slurry of the desired zeolite and dried at 
approximately 500 to 600.degree. C. Preferably coating takes place by 
suspension of the material utilized for coating having a large specific 
surface area with the addition of a binding agent and following sintering 
at a high temperature and, if necessary, in an inert gas atmosphere. 
Filling of the compressed gas storage means with gas and/or with the 
pyrotechnic charge is performed using known technology. 
Whereas the invention has been described with reference to a compressed gas 
storage means as a component of a gas bag module, the principle of the 
coating with a material having a high specific surface area can be 
employed in any other compressed gas storage means for vehicle occupant 
restraining systems.