GB2292788A

GB2292788A - A gas generator arrangement

Info

Publication number: GB2292788A
Application number: GB9417377A
Authority: GB
Inventors: Torbjorn Skanberg
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 1994-08-26
Filing date: 1994-08-26
Publication date: 1996-03-06
Also published as: GB9417377D0

Abstract

A gas generator for a vehicle safety device comprises a first housing (1) containing a pyrotechnic charge (2) and means (3) to ignite the charge, the latter being such that it generates a gas at least part of which is oxidisable. The arrangement includes a second housing (8) comprising a compressed gas at least part of which is oxygen. An outlet (5) from the first housing and an outlet (9) from the second housing lead to a combustion chamber (6) where the gases are mixed, on operation of the device, to effect oxidation of the oxidisable components of the gas from the pyrotechnic charge (2). The oxidation chamber (6) may be provided with a catalytic igniter (11). Gas from the oxidation chamber (6) is directed to the safety device (7). <IMAGE>

Description

DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO A GAS GENERATOR ARRANGEMENT" THE PRESENT INVENTION relates to a gas generator arrangement and more particularly relates to a gas generator arrangement intended to provide gas for a safety device within a motor vehicle, such as an air-bag or a seat-belt pretensioner.

It is increasingly common for vehicles to be provided with air-bags adapted to be inflated in the event that an accident should arise to provide protection for an occupant of the vehicle. It is also increasingly common for vehicles to be provided with seat-belt pretensioners which operate when an accident occurs.

Various types of gas generator have been proposed for use with such air-bags and pretensioners, but a typical gas generator utilises a pyrotechnic charge, such as, for example, a mixture of Nitrocellulose and Nitroglycerine.

Such a pyrotechnic charge, when ignited, rapidly produces a relatively large volume of gas. Unfortunately the gas itself may comprise a toxic component, such as carbonmonoxide, or a potentially explosive component, such as hydrogen.

This is undesirable, since the gas that is used to inflate the air-bag subsequently enters the passenger compartment of the motor vehicle. There is, therefore, a risk that an occupant of the vehicle may, subsequent to inflation of an air-bag, suffer from carbonmonoxide poisoning and also there is a risk that the hydrogen may explode.

The present invention seeks to provide an improved gas generator arrangement.

According to this invention there is provided a gas generator arrangement for a vehicle safety device, the gas generator comprising a first housing containing a pyrotechnic charge, and means to ignite the pyrotechnic charge, the pyrotechnic charge being such that, when ignited, it generates a gas at least part of which is oxidisable, and a second housing containing a compressed gas, at least part of which is an oxidising gas, outlets from the first housing and the second housing leading to a further chamber where, on operation of the arrangement, gas from the pyrotechnic charge and gas from the second housing are mixed to effect oxidation of the oxidizable components of the gas from the pyrotechnic charge, the further chamber having an outlet to be connected to the safety device.

Preferably the oxidising gas comprises oxygen.

Conveniently the gas within the second housing additionally comprises argon and also additionally comprises helium.

Argon is chosen to be a component of the gas within the second housing because argon has the property of absorbing heat.

At this stage it should be explained that it has been proposed previously to utilise a pyrotechnic charge as the main component of a gas generator, and also it has been proposed to use a bottle of compressed gas.

The use of a pyrotechnic charge is associated with disadvantages including (depending upon the precise nature of the pyrotechnic charge) a risk that hot particles of the pyrotechnic charge will be directed into an air-bag inflated by the charge, thus damaging the interior of the air-bag, and also a risk that the gas generated by the pyrotechnic charge is very hot and partially melts the inner lining of the air-bag. A further problem with the use of a pyrotechnic charge is that if the pyrotechnic charge is of a sufficient size to generate enough gas to inflate an air-bag, inadvertent ignition of the pyrotechnic charge may cause a substantial undesirable explosion.

Problems have arisen when pyrotechnic charges of this size have been inadvertently ignited during manufacture or during assembly of motor vehicles. The use of a bottle of compressed gas suffers from the disadvantage that when a gas is permitted to expand from a bottle of compressed gas, the temperature of the gas falls, meaning that a stream of very cold gas is generated. Cold gas occupies a low volume and/or only exerts a low pressure.

Consequently, it has been suggested to utilise a "composite" gas generator in which gas from a bottle of compressed gas is mixed with gas from a pyrotechnic charge.

The warm or hot gas from the pyrotechnic charge increases the temperature of the cool gas from the bottle of compressed gas. In a "composite" gas generator it is possible to use a smaller pyrotechnic charge, than in a gas generator where only a pyrotechnic charge is provided to generate gas to inflate an air-bag. The use of a smaller pyrotechnic charge is preferred since it is safer than the use of a larger pyrotechnic charge.

Thus, in one embodiment of the present invention, the second housing additionally contains argon which becomes admixed with the hot gas from the pyrotechnic charge. The argon absorbs heat well, and thus the temperature of the gas from the second housing is elevated, meaning that the gas will occupy a larger volume and/or exert a greater pressure.

The pyrotechnic charge may comprise a mixture of nitrocellulose and nitroglycerine.

Preferably the further chamber is provided with a catalytic igniter, preferably comprising a catalytic inner metal, such as a metal selected from the group comprising platinum, osmium, palladium, rhodium and ruthenium, the inner metal conveniently being supported on a porous substrate formed, for example, of alumina, asbestos of silica.

Alternatively, the further chamber may comprise a catalytic converter.

Advantageously the second housing is provided with an electrically actuated control valve and wherein the pyrotechnic charge is provided with an electrically triggered squib comprising said means to ignite the pyrotechnic charge, means being provided to connect the control valve and the squib to a crash sensor to activate both the squib and the control valve in the event that an accident occurs.

Conveniently a valve is provided which closes the outlet port from the second housing leading to the further chamber, the valve being opened in response to a rise of pressure caused by ignition of the pyrotechnic charge.

It is thus to be appreciated that, in operation of a gas generator in accordance with the invention as described above, the gas generated by ignition of the pyrotechnic charge, which contains oxidisable components, is mixed with an oxidising gas to effect substantially complete oxidation of the oxidisable components.

Consequently, the resultant gas is substantially free of carbonmonoxide and also substantially free of hydrogen.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which FIGURE 1 is a diagrammatic view of a gas generator arrangement associated with an air-bag constituting one embodiment of the invention, and FIGURE 2 is another corresponding diagrammatic view of another embodiment of the invention.

Referring initially to Figure 1 of the drawings, a gas generator arrangement for inflating an air-bag comprises a housing 1 containing a pyrotechnic charge 2.

The pyrotechnic charge may be of any appropriate pyrotechnic material which, when ignited, rapidly produces a large quantity of gas. The preferred pyrotechnic charge comprises a mixture of Nitrocellulose and Nitroglycerine which, when ignited, produces a mixture of gases which comprise 23% carbondioxide, 15% nitrogen, 42% carbonmonoxide and 20% hydrogen.

Contained within the housing 1 is an electrically triggered pyrotechnic igniter squib 3 which is connected to electric leads 4 which in turn are connected to a crash sensor (not shown). The arrangement is such that when a crash is sensed by the crash sensor an electric impulse is transmitted through the electric leads 4 to the igniter squib 3 which thus ignites the pyrotechnic material 2.

The housing 1 has an outlet conduit 5 which extends to a combustion chamber 6 (which will be described hereinafter), the combustion chamber 6 having an outlet leading directly to an air-bag 7. Consequently, when a crash is sensed by the crash sensor and the pyrotechnic material 2 is ignited, gas from the pyrotechnic material inflates the air-bag 7.

The described gas generating arrangement additionally includes a second housing in the form of a pressure vessel 8 which contains a compressed gas. At least part of the compressed gas comprises oxygen. It is preferred that the compressed gas also contains other inert gas and in one particular arrangement the vessel 8 contains 80% argon1 10% helium and 10% oxygen. It has been found that argon has good heat absorbing properties, whereas helium facilitates the detection of leaks.

An outlet port 9 from the pressure vessel is connected, through an electrically actuated valve 10 to the combustion chamber 6. The electrically actuated valve 10 is connected to the electric leads 4 which receive the signal from the crash sensor in such a way that when the crash sensor senses a crash the electrically controlled valve is opened.

Contained within the combustion chamber 6 is a catalytic igniter 11. The catalytic igniter comprises a catalytic inert metal, such as a metal selected from the group comprises platinum, osmium, iridium, palladium, rhodium and ruthenium supported on a porous substrate such as alumina, asbestos or silica. The preferred metal is platinum. The catalyst may be in the form of a thin film provided on the porous substrate, or may be present in the form of a block.

It is to be appreciated that in operation of the arrangement illustrated in Figure 1, when the crash sensor senses a crash the pyrotechnic charge 2 is ignited and also the electrically actuated valve is opened. The combustion gases from the pyrotechnic charge and the gas present within the pressure vessel are thus simultaneously directed towards the combustion chamber 6. The gas from the pyrotechnic charge is at an elevated temperature, and when mixed with the gas from the pressure vessel, which contains oxygen, the oxidisable components of the gas from the pyrotechnic charge are oxidised. Thus the hydrogen burns to form water and the carbonmonoxide is further oxidised to form a carbondioxide. The catalytic igniter provided as a precautionary measure to ensure that the oxidation reactions do occur.

Consequently, the gas leaving the combustion chamber 6 is fully oxidised and does not contain any significant quantities of carbonmonoxide or hydrogen.

Figure 2 illustrates a modified embodiment of the invention, many of the component parts being the same as in the embodiment of Figure 1. Like reference numerals are utilised for these parts which will not be re-described.

It is to be observed that in the embodiment of Figure 2 a mechanical valve 12 is provided which normally seals the outlet port 9 of the pressure vessel 8, the mechanical valve being opened in response to the generation of gas on ignition of the pyrotechnic material 2.

The valve 12, illustrated diagrammatically, comprises a valve element which, in an initial position, closes the outlet 5 from the housing 1 containing the pyrotechnic charge 2 and which also closes the outlet port 9 from the pressure vessel 8. The valve is such that when the pyrotechnic charge 2 is ignited, and gas at a relatively high pressure flows along the outlet 5 of the housing 1, the valve will move to an open position (shown in phantom in Figure 2) thus opening not only the outlet 5 from the housing 1 but also the outlet port 9 from the pressure vessel 8.

Whilst, in the embodiments described above, the combustion chamber 6 is provided with a catalytic igniter 11, the combustion chamber 6 could be replaced by a catalytic converter adapted to effect substantially cold combustion of the oxidisable components of the gas generated by the pyrotechnic material 2.

Whilst the invention has been described with specific reference to a gas generator for generating gas for an air-bag, it is to be appreciated that a gas generator of this type may be used for other purposes, such as to activate a seat-belt pretensioner.

Claims

CLAIMS:

1. A gas generator arrangement for a vehicle safety device, the gas generator comprising a first housing containing a pyrotechnic charge, and means to ignite the pyrotechnic charge, the pyrotechnic charge being such that, when ignited, it generates a gas at least part of which is oxidisable, and a second housing containing a compressed gas, at least part of which is an oxidising gas, outlets from the first housing and the second housing leading to a further chamber where, on operation of the arrangement, gas from the pyrotechnic charge and gas from the second housing are mixed to effect oxidation of the oxidisable components of the gas from the pyrotechnic charge, the further chamber having an outlet to be connected to the safety device.

2. An arrangement according to Claim 1 wherein the oxidising gas comprises oxygen.

3. An arrangement according to Claim 1 or Claim 2 wherein the gas within the second housing additionally comprises argon.

4. An arrangement according to any one of the preceding Claims wherein the gas within the second housing additionally comprises helium.

5. An arrangement according to any one of the preceding Claims wherein the pyrotechnic charge comprises a mixture of nitrocellulose and nitroglycerine.

6. An arrangement according to any one of the preceding Claims wherein the further chamber is provided with a catalytic igniter.

7. An arrangement according to Claim 6 wherein the catalytic igniter comprises a catalytic inert metal.

8. An arrangement according to Claim 7 wherein the catalytic inert metal is selected from the group comprising platinum, osmium, palladium, rhodium and ruthenium.

9. An arrangement according to Claim 7 wherein the catalyst is platinum.

10. An arrangement according to any one of Claims 7 to 9 wherein the inert metal is supported on a porous substrate.

11. An arrangement according to Claim 10 wherein the substrate comprises alumina, asbestos or silica.

12. An arrangement according to any one of Claims 1 to 5 wherein the further chamber comprises a catalytic converter.

13. An arrangement according to any one of the preceding Claims wherein the second housing is provided with an electrically actuated control valve and wherein the pyrotechnic charge is provided with an electrically triggered squib comprising said means to ignite the pyrotechnic charge, means being provided to connect the control valve and the squib to a crash sensor to activate both the squib and the control valve in the event that an accident occurs.

14. An arrangement according to any one of Claims 1 to 12 wherein a valve is provided which closes the outlet port from the second housing leading to the further chamber, the valve being opened in response to a rise of pressure caused by ignition of the pyrotechnic charge.

15. A gas generator arrangement substantially as herein described with reference to and as shown in Figure 1 of the accompanying drawings.

16. An arrangement substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawings.

17. Any novel feature or combination of features disclosed herein.