WO2009139677A1

WO2009139677A1 - Dual-stage airbag inflator

Info

Publication number: WO2009139677A1
Application number: PCT/SE2008/050559
Authority: WO
Inventors: Kjell Enevoldsen; Robert Odwong
Original assignee: Autoliv Development Ab
Priority date: 2008-05-14
Filing date: 2008-05-14
Publication date: 2009-11-19

Abstract

The present invention relates to a dual-stage airbag inflator (1) comprising a first chamber (3) containing a first combustible charge (6) for generating inflation gas and heat during combustion, a second chamber (4) containing a second combustible charge (7) for generating inflation gas during combustion, a partition (5) separating said chambers (3, 4) from each other, an ignition device (13) adapted to initiate combustion of said first combustible charge (6) for inflating an airbag in a first stage and means to initiate combustion of said second combustible charge (7) for inflating the airbag in a second stage, said second stage being subsequent to said first stage. The partition (5) is made of a heat conductive material to conduct heat from said first chamber (3) to said second chamber (5) and constitutes said means for initiating combustion of said second combustible charge (7). The present invention aims at providing an improved dual-stage airbag inflatornot being bulky and complex.

Description

DUAL-STAGE AIRBAG INFLATOR

Technical field

The present invention relates to a dual-stage airbag inflator comprising a first chamber containing a first combustible charge for generating inflation gas and heat during combustion, a second chamber containing a second combustible charge for generating inflation gas during combustion, a partition separating said chambers from each other, an ignition device adapted to initiate combustion of said first combustible charge for inflating an airbag in a first stage and means to initiate combustion of said second combustible charge for inflating the airbag in a second stage, said second stage being subsequent to said first stage.

Technical background

Airbag inflators are well known in the art of motor vehicles for use with passive restraint systems in order to protect the vehicle occupants in case an accident occurs. Upon actuation of the restraint system the airbag is inflated with gas produced or supplied by the airbag inflator. Dual-stage inflators, i.e. inflators having two or more gas-generating charges that are subsequently activated, are often used to achieve a desired inflator performance and a proper inflation of the airbag. Normally, the gas-generating charges are stored in different chambers separated from each other by means of an insulating wall preventing activation of the second charge upon flames and/or heat from combustion of the first charge. Means for initiating combustion of the second charge is then needed. Subsequent activation of charges in a dual-stage inflator may be realized by separate ignition devices connected to each individual charge.

The inclusion of a second ignition device increases one or more of the size, cost and weight of the inflator device.

Alternatively, heat generated during combustion of the first charge may be used to initiate combustion of the second charge to overcome the need of a second ignition device. In US 2005/0161926 A1 such a solution is disclosed, where an ignition enhancement apparatus for sympathetically igniting a second gas generant composition in response to combustion of a first gas generant composition ignition apparatus is included. This solution is however considered complex and involves several sensitive steps which may result in difficulties to achieve a proper ignition of the second gas generant composition.

Summary of the invention

It is an object of the present invention to overcome the above described drawbacks, and to provide an improved dual-stage airbag inflator.

This and other objects that will be apparent from the following summary and description are achieved by a dual-stage airbag inflator according to the appended claims.

According to an aspect of the present invention, there is provided a dual-stage airbag inflator comprising a first chamber containing a first combustible charge for generating inflation gas and heat during combustion, a second chamber containing a second combustible charge for generating inflation gas during combustion, a partition separating said chambers from each other, ignition device adapted to initiate combustion of said first combustible charge for inflating an airbag in a first stage and means to initiate combustion of said second combustible charge for inflating the airbag in a second stage, said second stage being subsequent to said first stage. The partition is made of a heat conductive material to conduct heat from said first chamber to said second chamber and constitutes said means for initiating combustion of said second combustible charge.

A dual-stage airbag inflator based on one single ignition device is provided. Since the partition separates, and thereby forms a barrier between, the chambers, undesired activation of the second combustible charge upon flames from the combustion of the first combustible charge is prevented. The partition is adapted to constitute means for initating combustion of a second combustible charge, which means that no additional ignition device is needed in order to realize subsequent ignition of the charges. Thus, a inflator having few parts is provided. Furthermore, a cost-effective inflator being easy to assemble is provided. Since heat is conducted through the whole surface separating the charges effective heat conduction is achieved, which provides a controlled and stable ignition of the second charge. Hence, a predetermined time-delay between activation of the charges is enabled. The predetermined time-delay is determined by the selected partition material and the characteristics of the partition, such as diameter, contact surface area and thickness. It is thus possible to adapt the inflator for a certain application.

The partition is preferably made of a material having a heat conductivity coefficient large enough to conduct a sufficient amount of heat to initiate combustion of the second charge within a certain time interval.

Preferably, the partition is made of a metallic material, such as, for instance, copper, steel or aluminium.

The partition may be made of a flexible material, preferably an aluminium foil, in order to increase the heat conducting surface of the partition and consequently reduce the time delay between the stages. Furthermore, "dead volume" in each of the chambers where the combustible charges are stored can be reduced.

Preferably, the partition is arranged in a gas-tight manner in order to avoid unintentional ignition through hot gas distribution from the first chamber to the second chamber.

A material or substance having a pre-defined self-ignition temperature may be arranged on the surface of the partition facing the second chamber to enable further possibilities as regards tuning of the time-delay before initiating combustion of the second charge. Such a material may be solid, liquid, gaseous, a powder or having a granular shape.

Preferably, the dual-stage airbag inflator further comprises a pressure chamber containing pressurized gas, said pressure chamber being in fluid communication with said chambers. Thus, a low onset at the beginning of the gas inflation is realized, which is advantageous in order to avoid agressivity to the airbag.

Brief description of the drawings

The present invention will now be described in more detail with reference to the accompanying schematic drawing which shows a preferred embodiment of the invention and in which: Fig. 1 shows a sectional view of a an airbag inflator according to an embodiment of the present invention.

Detailed description of preferred embodiments Fig. 1 shows a dual-stage airbag inflator 1 according to an embodiment of the present invention. In this case the inflator 1 is a hybrid inflator, i.e. gas generated from pyrotechnical charges in combination with pressurized gas stored within the inflator are used to inflate an airbag. The dual-stage airbag inflator 1 , which is formed by a cylindrical housing 2 made of steel, comprises a first combustion chamber 3, a second combustion chamber 4 and a partition 5 separating the combustion chambers 3 and 4 from each other. A first combustible charge 6 capable of generating inflation gas and heat is stored in the first combustion chamber 3 and a second combustible charge 7 capable of generating at least inflation gas is stored in the second combustion chamber 4. The charges 6 and 7 may be of the same or of different types. The person skilled in the art realizes that applicable gas generating charges known in the art, such as charges in form of pellets, grain or wafers can be used. The inflator 1 further comprises a sealed pressure chamber 8, in which pressurized gas 9, such as, for example, oxygen, argon, helium, nitrous oxide (N₂O) and combinations thereof, is stored. The first combustible charge 6 is in contact with the pressurized gas 9 by a plurality of openings 10, which provide fluid communication between the first combustion chamber 3 and the gas-containing pressure chamber 8. Inflation gas generated by combustion of the first charge 6 is communicated through the openings 10, via the pressure chamber 8, to an outflow unit 11 , for inflating an airbag in a first stage together with compressed gas stored in the pressure chamber 8. The second chamber 4 is provided with openings 12 through which inflation gas, generated by combustion of the second charge 7, is communicated to the outflow unit 11 for inflating the airbag in a second stage. The inflator 1 further comprises an ignition device 13, of a type known in the art, adapted to initiate combustion of the first combustible charge 6 upon an electric signal from a sensor system (not shown) via a cable (not shown). Such a signal may for instance be generated by a crash sensor in response to a vehicle crash or roll rollover. Typically, such an ignition device 13 is designed to provide or produce an ignition discharge upon receipt of an electric signal. For this purpose the ignition device 13 includes a reactive pyro-charge (not shown).

The outflow unit 11 , which upon actuation of the inflator 1 receives inflation gas and communicates the inflation gas to an airbag, is arranged downstream the pressure chamber 8. There are different types of outflow units known in the art that are suitable. In this case, the outflow unit 11 comprises a nozzle 14 and a diffuser 15 having a plurality of openings 16 through which inflation gas is communicated to the airbag (not shown). In order to prevent the pressurized gas 9 from entering the airbag before actuation of the inflator 1 a burst disc 17 is arranged to seal the outflow unit inlet 18. Upon actuation of the inflator 1 the pressure inside the pressure chamber 8 is increased due to heat and gas generated from the charge 6, which causes the burst disc 17 to break, preferably at a certain predetermined pressure, thereby enabling inflation gas to enter the outflow unit 11 to be communicated to the airbag through the diffuser openings 16.

The partition 5 is arranged to separate and/or to form a barrier between the chambers 3 and 4. Thereby, the partition 5 prevents the second combustible charge 7 from, in an uncontrolled manner due to flames from combustion of the first combustible charge 6, being ignited. Such uncontrolled could result in undesired airbag inflation performance. The partition 5 is made of a material with the ability to distribute a thermal effect from the first combustion chamber 3 to the second combustion chamber 4. The partition 5 is thus made of a heat conductive material to, in a controlled way, conduct heat generated by the first combustible charge 6 to the second combustion chamber 4. By heat conducted through the partition 5, combustion of the second combustible charge 7 is initiated. The desired time delay before initiating the second charge may differ depending on the actual type of restraint system. The heat conducted through the partition 5 is depending on the partition material and the thickness of the partition 5. By, in the product development process, adapting the thickness and/or the material of the partition the inflator can be optimized for the actual type of application. In this case the partition 5 is made of steel. Preferred material and dimensions of the partition 5 is determined by the sensitivity needs for each application. Examples of other suitable materials are copper and aluminium. Due to heat conducted through the partition 5 combustion of the second charge 7 is initiated a pre-determined time after actuation of the first combustible charge 6.

In the following actuation of the airbag inflator 1 described above will be explained. Upon a signal from a sensor system (not shown) combustion of the first combustible charge 6 is initiated by the ignition device 13. During combustion of the first charge 6 heat and inflation gas is generated. Inflation gas is then received in the pressure chamber 8 through the openings 10. Consequently, the pressure in the expansion chamber 8 increases and at a certain level the burst disc 17 is broken, whereby the gas enter the outflow unit 11 and is communicated to the airbag (not shown) through the diffuser 5. The airbag is then inflated by the inflation gas. During combustion of the first charge heat is generated. A part of the heat generated upon combustion of the firs charge 6 is conducted to the second chamber 4. A predetermined time after after actuation of the first combustible charge 6, combustion of the second charge 7 is initiated due to heat conducted through the partition 5. During combustion of the second charge 7 further inflation gas is generated and communicated to the airbag through the openings 12 and the outflow unit 11. In this manner desired characteristics as regards the airbag behaviour and/or the pressure build-up during inflation is achieved.

A substance (not shown) arranged between the partition 5 and the second charge 7, which substance is ignited at a certain temperature, may be used in combination with the heat conductive partition 5 to initiate combustion of the second charge 7.

In an alternative embodiment a partition provided with perforations may be used in order to increase the heat conduction to the second combustion chamber 4. It should be noted that the size of such perforations need to be adapted in such a way that ignition of the second charge 7 is achieved in a controlled manner.

The inflator in embodiment 1 is "hybrid" in that it incorporates and/or utilizes both pressurized stored gas and a supply of gas-generating material to inflate an associated inflatable cushion (not shown) of an inflatable restraint system. Alternatively, the inflator 1 may be an inflator, in which all inflation gas is generated based on combustion of combustible charges, i.e. a pyrotechnical inflator. The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It will be appreciated that the described embodiment of the invention can be modified and varied by a person skilled in the art without departing from the inventive concept defined in the claims. It is realized by a person skilled in the art that features from various embodiments disclosed herein may be combined with one another in order to provide further alternative embodiments.

Claims

1. Dual-stage airbag inflator (1 ) comprising a first chamber (3) containing a first combustible charge (6) for generating inflation gas and heat during combustion, a second chamber (4) containing a second combustible charge (7) for generating inflation gas during combustion, a partition (5) separating said chambers (3, 4) from each other, an ignition device (13) adapted to initiate combustion of said first combustible charge (6) for inflating an airbag in a first stage and means to initiate combustion of said second combustible charge (7) for inflating the airbag in a second stage, said second stage being subsequent to said first stage, characterized in that the partition (5) is made of a heat conductive material to conduct heat from said first chamber (3) to said second chamber (5) and constitutes said means for initiating combustion of said second combustible charge (7).

2. A dual-stage airbag inflator (1 ) according to claim 1 , wherein the partition (5) is made of a metallic material.

3. A dual-stage airbag inflator (1 ) according to any of claims 1-2, wherein the partition (5) is made of a flexible material, preferably an aluminium foil.

4. A multiple-stage airbag inflator (1 ) according to any of claims 1 -3, wherein the partition (5) is arranged in a gas-tight manner.

5. A multiple-stage airbag inflator 1 according to any of claims 1-4, wherein a material having a pre-defined self ignition temperature is arranged on the surface of the partition (5) facing said second chamber 4.

6. A dual-stage airbag inflator 1 according to any of claims 1-5, further comprising a pressure chamber (8) containing pressurized gas (9), said pressure chamber being in fluid communication with said first chamber.