Gas generator

Land vehicles – Wheeled – Attachment

Reexamination Certificate

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Reexamination Certificate

active

06189925

ABSTRACT:

The invention relates to a gas generator for an airbag system of a vehicle, comprising a combustion chamber to accommodate a propellant which is able to be activated, which chamber has outflow openings for a gas which is generated after the propellant is activated, the outflow openings inside the combustion chamber being covered by a filtering device.
Such a gas generator has become known through the U.S. Pat. No. 4,561,675.
In the case of a hard impact of a motor vehicle, so-called gas generators of an airbag system generate gas to fill an airbag which then protects a vehicle occupant from impact onto hard interior parts of the vehicle such as the steering wheel or the side panels. These gas generators are generally of a pyrotechnic nature, so that through a current impulse by the sensor arrangement detecting a vehicle crash, an ignition unit is activated. The igniting of the so-called ignition charge generates hot particles which then strike onto the surface of a propellant which is generally present in tablet form, which then itself ignites and burns down in the so-called combustion chamber under a high pressure. Through the burning of the propellant, a gas is produced for filling the airbag. Since in addition to pure gas, fluid or solid components are also produced during combustion, corresponding filters are also provided in the housing of the gas generator, through which the gas stream is purified before emerging from the gas generator.
In the known gas generator, outflow openings are provided in a housing wall, through which the gas which is generated can flow out from the combustion chamber. Immediately in front of the outflow openings, there are filtering devices which cover the outflow openings and lie against the inner face of the housing wall of the combustion chamber. The known filtering device is constructed in two parts so that it is composed of two layers of different filtering material. The filtering device serves to prevent the outflow openings from being able to clog due to the propellant tablets. Furthermore, through the filtering device combustion residues are retained inside the combustion chamber.
Through the direct arrangement of the filtering device in front of the outflow openings, a reduction to the flow cross-section of the outflow openings occurs. This becomes all the more noticeable as it corresponds to the mesh width and the pore size of the filtering material of the filtering device, respectively. Basically, an impairment to the gas inflow into the outflow openings exists through the filtering material lying immediately in front of these.
Owing to the flow effect of the outflow openings, the filtering material is only flowed through in the region of the outflow openings. The remaining filtering material of the filtering device, on the other hand, is largely unused. Consequently, a high stressing of the filtering material occurs in the region of the outflow openings. In extreme cases, punching out or perforated patterns inside the filter material can occur. In these cases, the gas developing in the combustion chamber can flow out from the combustion chamber almost unhindered.
Generally, the filtering device is produced from a filtering material which is not flexible, but rather is rigid. In addition, the rigid filtering material lies firmly against the inner wall of the housing. Hence, the propellant tablets can not be accommodated so as to be padded or biased by the filtering device. Relative movements can occur between the individual propellant tablets, which cause noises (rattling).
From the U.S. Pat. No. 5,291,178 a further gas generator is known, in which likewise filtering devices are fastened directly in front of the outflow openings. To improve the temperature conditions in the region of the outflow openings, in this gas generator an additional dividing wall is provided, which keeps the propellant tablets away from the outflow openings. In the region of the dividing wall, further flow channels are constructed, which in turn are coupled with filtering systems, so that this gas generator is complicated in its construction. Through the direct arrangement of the filtering device in front of the outflow openings, this gas generator also has the above-mentioned disadvantages with regard to the flow conditions in the region of the outflow openings.
In other gas generators, therefore, simple grid networks are provided as a filtering device in front of the outflow openings. The disadvantages of these solutions lie in that through the grid networks, which likewise lie directly in front of the outflow openings, the effective flow cross-section is reduced depending on the wire thickness. Since for this reason the wire diameter can not be selected to be very great, the hot gas stream from the combustion chamber leads to the wire frequently melting directly in front of the outflow openings. Then hot metallic particles also arrive at the exterior. Likewise, in turn, only the parts of the wire grid network are stressed which are provided in the region of the outflow openings.
Through the DE 40 12 893 A1 therefore a technical teaching is proposed of securing several layers of steel wool in front of the outflow openings in a gas generator. The steel wool is of course in turn arranged directly in front of the outflow openings, so that here also in turn the same above-mentioned problems are to be found with regard to the flow cross-sections. Here, also, the parts of the steel wool which are situated in the region of the flow cross-sections of the outflow openings are stressed to an intensified extent.
It is therefore an object of the present invention to further develop a gas generator of the type initially mentioned such that the filtering process by the filtering devices in the region of the outflow openings becomes more reproducible and is improved, that a better utilization of the filtering material exists and a greater lifespan of the filtering device is achieved.
The problem is solved according to the invention in a surprisingly simple manner in that the filtering device is arranged spaced apart from the outflow openings, and that the filtering device divides the combustion chamber in axial direction or also in radial direction into a combustion chamber for the propellant and into one or more expansion chambers for the developing gas.
Through the spaced arrangement of the filtering device from the outflow openings, no reduction takes place of the flow cross-sections in the region of the outflow opening and the filtering material of the filtering device can be flowed through better. Consequently, the filtering material of the filtering device becomes more uniform and is utilized over the entire region of the filtering device. The utilization of the filtering material is only still determined here by the pore- or mesh size of the filtering material.
Owing to the more uniform flow processes inside the filtering device, an improved temperature distribution is brought about inside the filtering device. Therefore, individual partial regions of the filtering device can be prevented from being thermally stressed too intensively.
The filtering device now divides the combustion chamber into a combustion space and one or more expansion chambers. It is preferred to use a flexible or elastic filtering material for the filtering device. If in fact pressure peaks build up inside the combustion space, the filtering device can yield in the direction of the expansion chamber. Pressure peaks in the combustion space can be easily reduced thereby, so that a pressure relief is brought about. For example, the filtering device can be secured inside the combustion chamber only at the top and bottom so that the central region of the filtering device can bulge. It is also conceivable that the filtering device is arranged displaceably inside the combustion chamber, in order to be able to react to pressure changes.
Through the free space (expansion chamber) in front of the outflow openings, the utilizable flow cross-section of the filtering device is no longer influenced so great

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