GB2416199A

GB2416199A - Inflator for a vehicle airbag

Info

Publication number: GB2416199A
Application number: GB0415575A
Authority: GB
Inventors: Peter Qvint; Mats Karlin; Mats Johansson
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2004-07-12
Filing date: 2004-07-12
Publication date: 2006-01-18
Anticipated expiration: 2024-07-12
Also published as: GB2416199B; GB0415575D0

Abstract

An inflator (1) for inflating an air-bag, the inflator (1) having a first gas bottle (5) and a second gas bottle (6). Each of the gas bottles (5,6) has an outlet (13,14) which is covered by a membrane (15,16). The membranes (15,16) are deformable and positioned opposite one another, so that when the gas bottles (5,6) are filled with gas, the membranes (15,16) deform and touch one another, so that each membrane (15,16) exerts a force on the other membrane (15,16). The inflator (1) also incorporates an opening unit (19) which comprises a pyrotechnic charge (22) and an opening piston (27). The inflator (1) is actuated by igniting the pyrotechnic charge (22), which generates a volume of gas to move the opening piston (27) to a position where the opening piston (27) ruptures one or both of the membranes (15,16). The mixture of gases from the gas bottles (5,6) may be ignited, and a large volume of gas is generated, which passes out of the inflator (1), through a deflector (2), to inflate the air-bag.

Description

PATENTS ACT 1977 PI 8734GB-NF/DMR/jsd/ns/md

DESCRIPTION OF INVENTION

"IMPROVEMENTS IN OR RELATING TO AN INFLATOR" THE PRESENT INVENTION relates to an inflator, and more particularly relates to an inflator for an air-bag for use in a motor vehicle.

It has been proposed previously to provide an inflator which has two separate gas chambers, each containing a different gas, with one gas including an oxidisable gas and the other gas including an oxidising gas. Each of the gases on their own is stable.

Upon actuation of the inflator each gas is released from its respective chamber, into a gas flow path within the inflator, where the two gases mix. The mixture of the two gases is then ignited and generates heat. A substantial volume of gas is generated to inflate the air-bag.

An inflator of this type is disclosed in GB 2,373,310.

In order for an inflator of this type to function correctly, the two gases must be well mixed. Otherwise, if there is a higher concentration of one gas than the other gas, some of the gas of higher concentration will be left un- reacted, resulting in the volume of gas being generated from the reaction of the gases not being optimised. An incorrect volume of gas produced by the inflator will inflate the air-bag to an incorrect pressure, which may be potentially very dangerous in an accident situation, as the air-bag will no longer provide the correct level of protection for a vehicle occupant.

To ensure that the gases from each of the chambers are well mixed, and to ensure that there is not a higher concentration of one gas than the other in the mixture, it is important that the gases are released from the chambers at the same time. The inflator disclosed in GB 2,373,310 incorporates an actuating element, which when actuated, moves a pair of opening elements, which in turn break sealing elements on each of the chambers to release each of the gases.

Although this prior art inflator intends to solve the problem of releasing the two gases from the chambers simultaneously, it utilises several moving parts to do so, thus making the design of the inflator relatively complex. The complex design is expensive to manufacture.

The present invention seeks to provide an improved inflator.

According to the present invention there is provided an inflator for inflating an air-bag, the inflator comprising a first bottle containing a first gas and a second bottle containing a second gas, the first bottle having an outlet which is sealed by a first membrane and the second bottle having an outlet which is sealed by a second membrane, each bottle being positioned so that the outlet of one bottle is facing the outlet of the other bottle, wherein the pressure of gas within the bottles deforms the membranes towards each other so that an area of each said membrane exerts a force on the other membrane, the inflator also incorporating a moveable element which is moveable in response to a predetermined signal from a first position to a second position in which at least part of the element engages and ruptures at least one of the said membranes to release the gas from the bottles.

It is believed that the rupturing of one membrane will open the first bottle, and the second membrane, no longer being supported from the exterior, and also being subjected to a flow of gas from the first bottle, will also rupture.

However, it is preferred that the moveable element, when in the second position, engages and ruptures both of the membranes. An arrangement of this type will ensure, beyond all doubt, that both membranes will rupture at substantially the same instant.

Preferably the inflator incorporates a mixing chamber in which, upon actuation of the inflator, the first gas and the second gas mix, the inflator also incorporating a gas flow path so that a gas mixture may flow from the mixing chamber and out of the inflator.

In one embodiment the moveable element is a piston and the inflator incorporates a pyrotechnic charge contained within a pyrotechnic chamber which, when actuated, produces a volume of gas to move the piston.

In another embodiment the moveable element is resiliently biased towards the second position, and the inflator incorporates a releasable retaining member to retain said movable element in said first position before the inflator is actuated, there being means to move the retaining member to release the moveable element in response to said predetermined signal.

Preferably a coil spring resiliently biases the piston towards the sealing arrangement.

Conveniently the area of each membrane that exerts a force on the other membrane is substantially planar.

Advantageously the first membrane is in direct contact with the second membrane when the membranes are deformed.

Preferably the inflator incorporates a deflector to deflect gas flowing out of the inflator.

With the outlets of the two bottles facing each other, there may be a substantial angle, up to, approximately, 60 between the axes of the two bottles.

However, it is preferred that the outlet of one bottle is substantially opposite the outlet of the other bottle. In this way the forces applied to the membranes by the gases inside the bottles are directed in opposite directions, thus effectively balancing each other out.

In one embodiment of the invention both the first gas and the second gas are substantially inert.

However, in a preferred embodiment of the invention the first gas includes an oxidisable agent and the second gas includes an oxidising agent.

The oxidisable agent may be selected from a gaseous hydrocarbon or mixtures thereof.

Preferably the gaseous hydrocarbon is selected from H2, CH4, C2H6, C3 He, C4H'o or mixtures thereof.

The first gas may include an inert gas.

Conveniently the second gas includes oxygen, air or nitrous oxide as the oxidising agent, and the second gas may include an inert gas.

The or each inert gas may be selected from Ar, He, N2 or CO2.

Preferably means are provided to ignite a gas mixture that has flowed out of the inflator.

Conveniently the means provided to ignite the gas mixture that has flowed out of the inflator only ignites the gas mixture after the gas bottles are substantially exhausted.

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 sectional view through an inflator in accordance with a preferred embodiment of the present invention, with the inflator in a normal condition, without having been actuated, FIGURE 2 is a view of the inflator shown in Figure 1, after the inflator has been actuated, but before the opening element has opened the closures, and FIGURE 3 is a view corresponding to Figure 1, after the inflator has been actuated, and after the opening element has opened the closures.

Referring initially to Figure 1, an inflator 1, in accordance with a preferred embodiment of the present invention, has a generally cylindrical open-ended tubular housing 2, with an upper aperture 3 and a lower aperture 4 positioned diametrically opposite one another in the central part of the housing 2. One of a pair of identical gas bottles 5,6 is mounted to each end of the housing 2, with each bottle 5,6 having a top portion extending partially into the housing 2 and closing an open end of the housing 2.

The bottles 5,6 each have a generally planar base 7, 8, with each base 7, 8 having a normally closed filling port 9,10 positioned at the centre.

The filling ports 9,10 are each used for filling a respective bottle 5,6 with gas.

The bottles 5,6 each have a generally planar top wall 11,12. Each of the top walls 11,12 has an outlet aperture 13,14 at its centre. A gas-tight membrane 15,16 is attached to each of the top walls 11,12, on the upper surface of the top wall 11,12, and positioned so that each membrane 15,16 covers the outlet aperture 13,14 of the bottle 5,6. The membranes 15,16 form a sealing arrangement.

When the inflator 1 is manufactured, the bottles 5,6 are inserted into the housing 2 so that the top portion of each bottle 5,6 extends partially into an open end of the housing 2, with the outlet apertures 13, 14 facing each other directly and thus being directly opposite one another. The bottles 5,6 are fixed in place and a gas tight seal is created between the outer edge of each of the bottles 5,6 and the inner edge of the housing 2.

The top walls 11,12 of the bottles 5,6 and the wall of the housing 2 together define a pre-mixing chamber 17. Once the bottles 5,6 have been secured to the housing 2, the bottles 5,6 are simultaneously filled with gas through their respective filling ports 9,10. In the preferred embodiment one of the gases has an oxidisable component such as hydrogen (H2), methane (CH4), ethane (C2H6), propane (COHN) or butane C4Ho or mixtures thereof and the other gas has an oxidising component such as air oxygen or nitrous oxide or mixture thereof. However, the gases may alternatively be any type of gas which may react with each other when mixed. The gases in each of the bottles 5,6 may themselves be mixed with an inert gas such as argon (Ar), helium (He), nitrogen (N2) or carbon dioxide (CO2).

As the bottles 5,6 are filled with gas, the pressure of the gas within the bottles 5,6 causes the membranes 15,16 to deform, outwardly from the top walls 11,12 of the bottles 5,6 and towards each other, until the membranes touch. The pressure of gas within the bottles 5, 6 may be such that the gas is at least partially liquefied.

When the bottles 5,6 are filled with gas, the membranes 15,16 are each deformed sufficiently so that the membranes 15,16 are pressed against each other, as shown in Fig. 1. Although in this preferred embodiment, the membranes 15,16 are shown to be in direct contact with one another, they may alternatively have another element between them, but with each of the membranes 15,16 still exerting force on the other membrane 15,16. In this preferred embodiment the membranes 15,16 deform upon contact with each other so that the force exerted by one membrane 15,16 on the other membrane 15,16 is spread over a substantially planar area 18. Preferably the gas pressure is the same in each of the gas bottles 5, 6.

An opening unit 19 is fixed in place within the lower aperture 4 of the housing 2, so that a part of the opening unit 19 extends through the lower aperture 4 and into the mixing chamber 17.

The opening unit 19 has a cylindrical open ended hollow body 20, which is located on the exterior of the housing 2. A sealing cap 21 is fixed to the body20 to close the open end of the body 20. The sealing cap 21 holds a pyrotechnic charge 22 in a position within a chamber defined within the hollow body 20.

At the opposite end of the body to the sealing cap 21 a hollow cylindrical neck 23, of smaller diameter than the diameter of the body 20, extends from the body 20. The neck has an aperture 26 in its end wall. The neck 23 extends through the lower aperture 4 of the housing 2 so that the neck 23 is located within the chamber within the hollow body 20.

A piston 27 is mounted for sliding movement within the opening unit 19.

The piston 27 incorporates a head 28 and a stem 29. The head 28 is of larger diameter than the stem 29 of the piston 27. The head 28 is a sealing sliding fit within the neck 23, and the stem 29 extends through the aperture 26 provided in the end wall of the neck 23. The piston 27 has an initial position in which the head 28 is located between the ignition apertures 24,25 and the chamber 20, and the stem 29 projects from the aperture 26 in the end wall of the neck 23 in alignment with, but spaced from, the membranes 15,16.

A cup shaped deflector 30 is fixed to the housing 2, on the opposite side of the housing 2 to the opening element 19. The deflector 30 has a cylindrical side-wall. The deflector 30 covers the upper aperture 3. The deflector 30 has vent apertures 31 formed in its side wall. A gas flow path exists from the mixing chamber 17, through the upper aperture 3, and through the vent apertures 31 in the deflector 30. The inflator will typically be used as an inflator for an air-bag in a vehicle and will be mounted within the air-bag. The gas flow path will thus extend to the interior of the air-bag. The deflector 30 may contain a gas filter to remove any particles from gas which is being vented.

Associated with the inflator, there will be igniter means to ignite the gas passing from the inflator to the interior of the air-bag. Many different types of igniter means may be used. A separate pyrotechnic device may be mounted within the interior of the air-bag to generate a flame to ignite the gas.

Alternatively a gas channel (not shown in Figure 1) may be provided extending from the chamber within the body 20 to the interior of the airbag thus igniting the gas mixture in the bag. When a pyrotechnic charge is provided in the interior of the air-bag, the pyrotechnic charge may be connected to the pyrotechnic charge 22 by means of an insulated pyrotechnic cable which will burn internally in a predetermined period of time, thus initiating the pyrotechnic charge which in turn will ignite the gas mixture in the bag.

It is also possible to have the pyrotechnic charge to ignite the gas located within the chamber 17. If such a location is used care must be taken to ensure that the pyrotechnic charge is only actuated after the gas bottles are substantially exhausted, in order to avoid premature combustion in the chamber 17 which could prove to be very disadvantageous.

It is envisaged that in a preferred embodiment of the invention the actuation of the pyrotechnic charge used to ignite the gas may be controlled by a controller which is responsive to parameters such as the position of the occupant, the weight of the occupant, or whether a childseat has been mounted adjacent the air-bag or not. It is to be understood that it may be preferable, in many circumstances, not to ignite the gas mixture, but instead to rely on the intrinsic volume of the mixed gases to inflate the air-bag. The air-bag would thus be inflated to a "soft" condition which may be appropriate if the occupant to be protected is leaning forwardly (occupant being out of position) at the instant of deployment of the air-bag.

The inflator 1 is actuated by igniting the pyrotechnic charge 22. The charge 22 may be ignited in response to a signal from an appropriate sensor.

Once ignited, the pyrotechnic charge 22 burns and produces a volume of gas in the chamber within the body 20 of the opening unit 19. As the gas pressure within the chamber of the body 20 rises, a force is exerted, on the lower side of the head 28 of the piston 27 as shown in Figure 1. The force exerted by the gas causes the piston 27 to move upwardly, and slide within the neck 23 of the opening unit 19, with the stem 29 of the piston 27 moving outwardly from the aperture 26 in the end wall of the neck 23. As the stem 29 of the piston 27 moves from the first position further outwardly from the neck 23 into the pre mixing chamber 17, the stem 29 of the piston 27 contacts the membranes 15,16, as shown in Figure 2. The piston 27 eventually reaches the second position and ruptures one or both of the membranes 15,16, as shown in Figure 3.

It is possible that the stem 29 of the piston 27 will rupture both of the membranes 15,16 simultaneously. However, should the piston27 come into contact with, and rupture, one of the membranes 15 before contacting the other membrane 16, the ruptured membrane 15 will not longer exert a force on the unruptured membrane 16. Thus, the unruptured membrane 16 will be deformed further by the pressure of gas within its associated gas bottle 6, and will deform sufficiently so that it also ruptures, or so that it is brought into contact with the stem 29 of the piston 27, which will cause the membrane to rupture.

Hence, even if the piston 27 only initially ruptures one of the membranes 15, 16, the configuration of the sealing arrangement will ensure that the other membrane 15,16 also ruptures with, at the worst, only a very short delay.

When both of the membranes 15,16 have ruptured, the gases within the gas bottles 5,6 will be released from the outlet apertures 13,14 and into the mixing chamber 17. Thus, the first gas from the first gas bottle 5,6 will mix with the second gas from the second gas bottle 5,6.

The gas continues to flow along the gas flowpath 32, through the gas filter in the deflector 30 and out into an air-bag in which the inflator 1 is mounted in order to inflate an air-bag.

Once the mixed gas has flowed into the air-bag, the gas may be ignited by the flame producing pyrotechnic unit. As the gas is ignited the temperature of the gas rises substantially causing the gas to expand and thus increasing the pressure within the air-bag.

Although the moveable element has been described thus far as being a piston 27, the moveable element may alternatively be any other element which is slideably mounted within the neck 23. The moveable element may be resiliently biased towards a second position in which at least part of the element engages and ruptures at least one of the membranes 15,16. The moveable element may be biased by a resilient element such as a coil spring. In such an alternative embodiment in which the moveable element is biased towards the second position, the moveable element will be retained in the first position during normal operation, by a releasable retaining member. This alternative embodiment also incorporates a means to move the releasable retaining member to release the moveable element in response to a predetermined signal.

While the invention has been described with reference to an embodiment in which there is an oxidisable gas and an oxidising gas, it is contemplated that in alternative embodiments each of the gas bottles 5, 6 will be filled with an inert gas or a mixture of inert gases.

In the described embodiment the bottles are positioned with their outlets directly facing each other, with the axes of the bottles being aligned. The axes of the bottles may be offset, by up to 60 for example, with the outlets facing each other in a slightly oblique way. The membranes of the bottles will still be deformed towards each other so that each membrane exerts a force on the other membrane.

When used in this Specification and Claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS: 1. An inflator for inflating an air-bag, the inflator comprising a

first bottle containing a first gas and a second bottle containing a second gas, the first bottle having an outlet which is sealed by a first membrane and the second bottle having an outlet which is sealed by a second membrane, each bottle being positioned so that the outlet of one bottle is facing the outlet of the other bottle, wherein the pressure of gas within the bottles deforms the membranes towards each other so that an area of each said membrane exerts a force on the other membrane, the inflator also incorporating a moveable element which is moveable in response to a predetermined signal from a first position to a second position in which at least part of the element engages and ruptures at least one of the said membranes to release the gas from the bottles.
2. An inflator according to Claim 1 wherein the moveable element, when in the second position, engages and ruptures both of the membranes.
3. An inflator according to Claim 1 or Claim 2 wherein the inflator incorporates a mixing chamber in which, upon actuation of the inflator, the first gas and the second gas mix, the inflator also incorporating a gas flow path so that a gas mixture may flow from the mixing chamber and out of the inflator.
4. An inflator according to Claim 1 or Claim 2 and Claim 3 wherein the moveable element is the stem of a piston and the inflator incorporates a pyrotechnic charge contained within an ignition chamber which, when actuated, produces a volume of gas to move the piston.
5. An inflator according to Claim 1 or Claim 2 and Claim 3 wherein the moveable element is resiliently biased towards the second position, and the inflator incorporates a releasable retaining member to retain said movable element in said first position before the inflator is actuated, there being means to move the retaining member to release the moveable element in response to said predetermined signal.
6. An inflator according to Claim 5 wherein a coil spring resiliently biases the piston towards the sealing arrangement.
7. An inflator according to any one of the preceding Claims wherein the area of each membrane that exerts a force on the other membrane is substantially planar.
8. An inflator according to any one of the preceding Claims wherein the first membrane is in direct contact with the second membrane when the membranes are deformed.
9. An inflator according to any one of the preceding Claims wherein the inflator incorporates a deflector to deflect gas flowing out of the inflator.
10. An inflator according to any one of the preceding Claims wherein the outlet of one bottle is substantially opposite the outlet of the other bottle.
11. An inflator according to any one of the preceding Claims wherein both the first gas and the second gas are substantially inert.
12. An inflator according to any one of Claims 1 to 10 wherein the first gas includes an oxidisable agent and the second gas includes an oxidising agent.
13. An inflator according to Claim 12 wherein the oxidisable agent is a gaseous hydrocarbon or mixtures thereof.
14. An inflator according to Claim 13 wherein the gaseous hydrocarbon is selected from H2, CH4, C2H6, COHN, C4Ho or mixtures thereof.
15. An inflator according to any one of Claims 12 to 14 wherein the first gas includes an inert gas.
16 An inflator according to any one of Claims 12 to 15 wherein the second gas includes air oxygen or nitrous oxide as the oxidising agent.
17. An inflator according to any one of Claims 12 to 16 wherein the second gas includes an inert gas.
18. An inflator according to Claim 14, 15 or Claim 17 wherein the or each inert gas is selected from Ar, He, N2 or CO2.
19. An inflator according to any one of Claims 12 to 18 ad dependent on Claim 3 wherein means are provided to ignite a gas mixture that has flowed out of the inflator.
20. An inflator according to Claim 19 wherein the means provided to ignite the gas mixture that has flowed out of the inflator only ignites the gas mixture after the gas bottles are substantially exhausted.
21. An inflator substantially hereinbefore described with reference to and as shown in Figures 1 to 3 of the accompanying drawings.
22. Any novel feature or combination of features disclosed herein.