DE29708380U1 - Gas generator - Google Patents

Description

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PATENT ATTORNEYS Manzingerweg 7

EUROPEAN PATENT ATTORNEYS D-81241 Munich

EUROPEAN TRADEMARK ATTORNEYS Tel. +49 89 89 69 80

9 May 1997

TRW Occupant Restraint Systems GmbH
Industriestrasse 20
D-73551 Aldorf

Our reference: T 8115 DE
HD/Gl
10

Gas generator

The invention relates to a gas generator for activating a vehicle occupant restraint system, with at least two charges of a pyrotechnic substance, which can be ignited separately by an associated igniter.

Multi-stage gas generators are used to adapt the protective effect provided by a vehicle occupant restraint system to the circumstances of the accident, in particular the intensity of the vehicle impact, but also the position, size and weight of the occupant. The charges are arranged in separate chambers and can be activated selectively by an assigned igniter. When only one charge is activated, the gas generator has its lowest output. If a further charge is also activated, the increase in pressure of the gases generated can be determined by measuring the time delay with which the further charge is activated after the first. Regardless of this time delay, however, the same final pressure is always achieved after a given number of charges have been activated.

The present invention provides a gas generator in which the pressure of the gases generated by activating multiple charges can be continuously varied.

According to the invention, the charges are coupled together in such a way that when a first charge burns after activation of the igniter assigned to it, at least one further charge, whose igniter is not activated, burns with a delay. While in a conventional multi-stage gas generator the charges are strictly separated from one another in order to ensure their selective activation, in the gas generator according to the invention the charges are coupled together so that when a charge is activated at least one further charge also burns. However, the coupling between the charges is so low that the further charge burns much more slowly than the first. The further charge is therefore not ignited immediately, but indirectly via the first. If the igniter of the further charge is now also activated, the further charge also burns without delay, but a reduced final pressure is reached compared to simultaneous activation of both charges. The lowest final pressure occurs when the further charge is not ignited immediately and therefore burns with a delay and with reduced intensity. Although the additional charge produces approximately the same amount of gas even with delayed combustion as with immediate ignition, the gases produced with delayed combustion have a lower temperature. However, the temperature, along with the amount of gas, is crucial for the final pressure achieved.

The invention will now be explained in more detail with reference to the accompanying drawing. In the drawing:

Fig. 1 is a schematic diagram of the gas generator;

Fig. 2 is a diagram showing the pressure curve of a conventional two-stage gas generator; and

Fig. 3 is a diagram showing the course of the gas pressure in the gas generator according to the invention.

The gas generator shown only schematically in Fig. 1 contains a first chamber 12 and a second chamber 14 in a housing 10. The chambers 12, 14 each contain a charge of a pyrotechnic gas-generating substance. The chambers 12, 14 are separated from one another by a partially permeable partition wall 16. Each charge is assigned its own igniter 18 or 20.

Through outlet openings of the

The gases generated when the gas generator is activated reach a vehicle occupant restraint device, in particular an inflatable gas bag, via the housing 10 and also via filter devices and gas guides (also not shown).

In the diagram in Fig. 2, four curves are shown, which are labeled 1, 2, 3 and 4. The steepest pressure increase occurs when the second charge is ignited with only a slight delay compared to the first at time ti by activating the associated igniter.

In curve 2, the igniter of the second charge is activated at time t2, and in curve 3 at time t3. Regardless of the delay, however, curves 1, 2 and 3 reach the same maximum value. In curve 4, only the first charge is activated, which results in a correspondingly lower final pressure.

As can be seen from Fig. 3, a similar pressure curve results in the gas generator according to the invention if the second charge is ignited at time t1 after the first charge is activated. At time t2, however, the pressure increase has progressed further because, in addition to the first charge, which was ignited immediately by activating its igniter, the second charge also burns, but with reduced intensity because it is not ignited immediately; rather, the combustion of the first charge continues with a delay through the partition 16 into the second charge. If the igniter of the second charge is activated at time t2, an accelerated pressure increase occurs according to curve 2, which, however, reaches a lower final pressure because the combustion of the second charge is less intense and therefore takes place at a lower temperature. Curve 3 shows that a further reduction in the final pressure can be achieved by an even greater delay in the activation of the igniter of the second charge at time t3.

The lowest final pressure is obtained according to curve 4 when only the first charge is ignited directly and the second charge is only ignited indirectly through its coupling with the first charge. However, compared to curve 4 in Fig. 2, a higher final pressure is obtained because the burn-up of the second stage contributes to the final pressure, albeit to a lesser extent.

It is thus evident that by determining the delay with which the second charge is ignited relative to the first, the final pressure of the gas generator can be continuously varied.
10

Claims (4)

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PRINCE & PARTNER ^: ·"' ^: ·· ^! - &bull; · · &diams;
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· · PATENT ATTORNEYS
EUROPEAN PATENT ATTORNEYS
EUROPEAN TRADEMARK ATTORNEYS Manzingerweg 7
D-81241 Munich
Phone +49 89 89 69 80 9 May 1997 TRW Occupant Restraint Systems GmbH
Industriestrasse 20 5 D-73551 Alfdorf Our reference: T 8115 DE HD/HD Protection claims 1. Gas generator for activating a vehicle occupant restraint system, with at least two charges of a pyrotechnic substance, each of which can be ignited separately by an associated igniter, characterized in that the charges are coupled to one another in such a way that when a first charge burns after activation of the igniter associated with it, at least one further charge, the igniter of which is not activated, burns with a delay. 2. Gas generator according to claim 1, characterized in that each charge is arranged in a separate chamber of a housing and the chambers are separated from one another by a partially permeable partition wall. 3. Gas generator according to claim 1 or 2, characterized in that the gas pressure generated is continuously variable by determining the time delay with which the igniter of the further charge is activated after activation of the igniter of the first charge. 4. Gas generator according to one of the preceding claims, characterized by its use in an inflatable protective cushion.