DE19629104C1 - Circuit arrangement for igniting pyrotechnic igniters in gas generators for airbag systems - Google Patents

Abstract

Ignition of the ignitable material occurs via an ignition plasma formed by evaporated material of the ignition resistance (RL). In the ignition current circuit (1) a low loss inductivity (L) is provided. The time constants gamma X = RL x C (capacity) and gamma L = L/RL are approximately the same as the time period from switching on the ignition current circuit to the evaporation of the resistance. The ignition resistance is so geometrically dimensioned that after its evaporation on an evaporating area of ignition plasma is produced.

Description

The invention relates to a circuit arrangement for igniting ignitable material, in particular pyrotechnic igniters in Gasgenera gates of airbag systems, with an ignition circuit in which an ignition resistor R _L made of evaporable material and a capacitance C are seen before, the ignition of the ignitable Material takes place via an ignition plasma formed from ver vaporized material of the ignition resistor.

Such a circuit arrangement is for example by the US 5,179,248.

Gas generators, which also include hybrid gas generators, are used to in the event of a hard impact of a motor vehicle, a gas mixture for To fill an airbag. The airbag protects the vehicle insas before impact on hard vehicle interior parts such as the steering wheel or the Side panels.

So-called igniters are used to ignite these gas generators sets a primary charge from pyro via an electrical current pulse bring technical material to ignition. Known pyrotechnic An igniters are ignited by the fact that they are fed into a capacitor secured electrical energy via an electronic switch (transistor / Thyristor) is switched to a wire or thin film resistor that then heated by the current pulse and evaporated. This will detonated a pyrotechnic charge.

The circuit arrangement known from US 5,179,248 is used for ignition a thin-layer lighter, in which a n-Si layer (ignition resistance) is applied. There are two on this n-Si layer  Pads attached in the form of metal connections through a Gap are separated. When applying a voltage to the An End faces are formed in this gap by evaporation of the n-Si layer an ignition plasma over which an explosive located near the gap Material is ignited.

The current pulse is generated via a capacitor, the Capacity, however, is such that only the stored energy a fraction is used until the ignition resistor burns out and there with the current flow is interrupted.

However, there are applications where only the ignition capacitor little space is available and therefore due to the oversizing of the con should be dispensed with. In these cases, it is advantageous to Energy content of the capacitor completely to ignite the pyrotechni exploiting cargo.

Another major disadvantage of previously known circuit arrangements gene is that the current flow is interrupted as soon as the ignition resistance has evaporated. For maintaining an ignition plasma the available from the capacitor charge extends over the ignition path Residual tension is limited.

The present invention is therefore based on the object of a scarf to further develop the arrangement of the type mentioned at the beginning, that as much as possible the entire energy content of the capacitance or the condenser tors completely to ignite the ignitable material, especially the py rototechnical charge, can be used.

This object is achieved in that a low-loss inductance L is provided in the ignition current circuit that the time constants τ _C = R _L × C and τ _L = L / R _L approximately equal to the period from switching on the ignition circuit to evaporating the ignition resistor R. _L are, and that the ignition resistor R _{L is} dimensioned geometrically such that an ignition plasma is generated there after its evaporation on an evaporation path.

The circuit arrangement according to the invention thus has the essential advantage that the resistance R _{L is designed} in its geometric dimensions so that it evaporates when the energy content of the capacitance C egg nes capacitor has dropped to about half the original value. The inductance L is in turn dimensioned such that at the time when the resistance R _{L has} evaporated, the energy stored by the current flow in the inductance L has such an effect that the rising voltage with the circuit open over the vaporized or blown ignition resistor R _L a plasma is generated.

A similar but uncontrolled process takes place during the discharge capacitor due to a short circuit. A plasma is also created here spark, the inductance being formed by the short-circuit loop.

As a dimensioning guideline for the circuit arrangement according to the invention, the time constant τ = R _L × C should be equal to the time constant τ = R _L / L and that the layer thickness, the area of the layer and the heat dissipation of the ignition resistor R _{L are selected in} such a way that that the resistance R _{L has} evaporated after a period τ.

Circuit arrangements are already known in which a ver pleasure inductance in an ignition circuit is turned to prevent accidental ignition by electromagnetic waves However, in these cases the inductance and its loss factor are lower completely different criteria.

In the circuit arrangement according to the invention, the EMC (electr gnetic compatibility) -security achieved in that the circuit an order in a confined space and shielded.

Further advantages of the invention result from the description and the Drawing. Likewise, the above and the others Features listed according to the invention individually for themselves or to several can be used in any combination. The one shown and the described embodiment is not a final list to understand, but rather has exemplary character for the Schil change of the invention.  

The single figure shows the basic circuit of the circuit arrangement according to the invention for a pyrotechnic igniter in a gas generator of an airbag system, the ignition circuit being formed by a capacitor C, an ignition resistor R _L , an inductance L and an ignition switch S.

After the capacitor C has been charged via a resistor R _V , the electronic ignition switch S is closed. The resistance R _L is designed in its geometric dimensions so that it evaporates when the energy content of the capacitor C has dropped to about half the original value. The inductance L is dimensioned such that at this time the energy stored by the current flow in the inductance L affects such that the rising voltage when the circuit opens over the evaporated or blown ignition resistance R _{L forms} an ignition plasma. The pyrotechnic material (not shown) located near the ignition resistor R _L is ignited by the ignition plasma.

As a dimensioning guideline for this circuit arrangement, the time constant τ = R _L × C should be equal to the time constant τ = R _L / L and that the layer thickness, the area of the layer and the heat dissipation of the ignition resistor R _L are selected so that the ignition resistor R _L evaporates after τ seconds.

Claims (1)

Circuit arrangement for igniting ignitable material, in particular of pyrotechnic igniters in gas generators of airbag systems, with an ignition circuit ( 1 ) in which an ignition resistor (R _L ) made of evaporable material and a capacitance (C) are provided, the ignition of the ignitable material via an ignition plasma formed from evaporated material of the ignition resistor (R _L ), characterized in that a low-loss inductance (L) is provided in the ignition circuit ( 1 ) that the time constants τ _C = R _L × C and τ _L = L / R _L approximately equal to the period from turning on the ignition circuit (1) to the evaporation of the Wi derstands (R _L), and in that the ignition resistor (R _L) is such dimensioned geometric di that, after its evaporation on a evaporation stretch an ignition plasma is generated there.