GB2448300A - Igniter tube in air bag inflator apparatus - Google Patents

Abstract

An airbag inflator apparatus features two gas chambers (2,4 fig.1), one containing a combustible gas, the other containing an oxidising gas to aide combustion, the chambers meeting at frangibly sealed 20 mouths 18, leading into a mixing chamber 14. Upon activation, a hollow combustion tube 34 draws in the mixed gases, ignites them, and projects them towards and out of an upper portion 16,17 of the device and into an airbag or similar. The combustion tube 34 also doubles as an activation piston. Upon combustion of a pyrotechnic squib 22, the tube 34 displaces upwards, see transition from fig.3 to fig.4, breaking frangible seals 20, such as foil sheets, to open the mouths 18 of the two chambers.

Description

"AN INFLATOR FOR AN AIR-BAG" The present invention relates to an

inflator for an air-bag, such as an air-bag provided in a vehicle to provide protection for an occupant of the vehicle in the event of an accident.

It has been proposed to provide air-bag inflators which incorporate two bottles or pressure vessels containing gas under pressure, each bottle or pressure vessel having an outlet which is normally sealed by sealing means, which sealing means is displaced or ruptured in an emergency situation, for example by the firing of a pyrotechnic squib, to allow the gas to escape from the bottle into the airbag. In prior proposed inflators of this general type one gas bottle may contain a fuel, in the form of an oxidisable gas and the other bottle may contain an oxidising gas. The gases, when they escape from the gas bottles are mixed and are ignited by igniter means, whilst they are being passed to the air bag, or when the gases are within the air-bag, to effect complete inflation of the air-bag. GB2417066 discloses an inflator of this type.

It is an object of the invention to provide an improved air bag inflator, of the kind set out above, which provides improved reliability of ignition and burning of such gas mixture supplied to the connected air bag and which is nevertheless relatively simple in construction.

According to the invention there is provided an inflator for an airbag, comprising a bottle containing a pressurised oxidisable gas and a bottle containing a pressurised oxidising gas, the bottles being connected with a structure providing a mixing chamber, the bottles having respective discharge openings sealed by respective sealing means sealing off the interiors of said bottles from said chamber, the inflator including means which can be activated to cause or allow the seals provided by said sealing means to be broken to allow the gases from said bottles to pass into said chamber and thence via said air opening into such airbag, the inflator including an igniter comprising a pyrotechnic squib confined in structure including an igniter tube extending within said chamber and arranged so that when said seals are broken and the squib is ignited, burning gases from the squib will be discharged through said tube to ignite the mixture of gases discharged from said bottles, said tube being arranged to release ignition gases at a position that is favourable for a reliable ignition, such as a position of a preferred gas flow, mixing, turbulence and pressure.

The igniter tube may have one or more ports or holes in the wall thereof through which such gas mixture can be drawn into the tube by the flow of igniter squib gases therealong, to commence combustion of such gases from said bottles during transport of these gases along the igniter tube. The pre-combusted gas mix then ignites the rest of the gas flow.

The means for causing or allowing the seals provided by said sealing means to be broken to allow the gases from said bottles to pass into said chamber may include a piston moveable along a complementary cylinder by pressure of gases generated by said squib when the latter is ignited.

In this case the igniter tube is preferably carried by said piston and a restricted passage, restricted in cross-section as compared with the cross-section of said cylinder, is provided through said piston and communicates with the interior of said tube for conveying burning gases from the squib through the piston to said tube.

In an alternative embodiment, the igniter tube is carried by the cylinder containing the piston and the bore of said tube communicates with the interior of said cylinder via a transverse passage in the wall of said cylinder, at a location such as to be blocked by said piston in the normal inactive state of the assembly, but such as to be disclosed by movement of said piston when the squib is fired, to allow burning gases from the squib to be discharged through said tube to ignite the mixture of gases discharged from said bottles.

Preferably each gas bottle is sealed by a rupturable foil, said means which can be activated to cause or allow said seals to be broken including respective support members engaging the rupturable foils to maintain the rupturable foils in an un-ruptured state, each said support member being retained in position by a part carried by said piston which part directly engages the support member, the arrangement being such that movement of the piston along said cylinder as a result of firing the squib thereby moves said part carried by said piston past said support members, permitting the support members to move to positions in which the foils will rupture to permit gas to escape from the gas bottle.

Conveniently the fuel or oxidisable gas in one gas bottle comprises hydrogen, ethane, methane, propane or butane.

Advantageously the oxidisable gas is mixed with one or more inert gases.

Preferably the oxidising gas in the other gas bottle is air, oxygen or nitrous oxide.

Conveniently the oxidising gas is mixed with one or more inert gases.

The invention also relates to an air-bag provided with an inflator of the type described above.

An embodiment of the invention is described below by way of example with reference to the accompanying drawings in which: Figure 1 is a view in section showing part of an airbag inflator in accordance with the invention, Figure 2 is sectional view corresponding to Figure 1 of a variant, Figure 3 is a fragmentary sectional view of part of the inflator of Figure 1, to a larger scale and showing some parts omitted in Figure 1 and showing the apparatus in a normal, and activated condition, Figure 4 is a fragmentary sectional view corresponding to Figure 3 but showing the apparatus in the activated condition, Figure 5 is a cross-sectional view of a variant, in a normal, unactivated condition, and Figure 6 is a cross-sectional view corresponding to Figure 5 showing the variant apparatus in an activated condition.

Referring to Figure 1, an air-bag inflator comprises a first gas bottle 2 and a second gas bottle 4. In the arrangement shown, the second bottle 4 is the mirror-image of the first bottle 2. Each gas bottle 2, 4, has a respective base 6 at one end, a respective tubular side wall 8 and a planar end wall 10 at its end opposite the base 6. A respective filling aperture (not shown) is provided in each base 6. The ends of the gas bottles 2 and 4 opposite said bases 6 thereof are secured to a central housing 12 which defines, with respective opposing parallel spaced-apart planar end walls 10 of the bottles 2, 4, a mixing chamber 14. An upper part 16 of housing 12 forms a conduit extending from or forming part of the chamber 14. Upper part 16 is provided with openings for the exit of gas. In use, the upper end 16 of the housing 12, with said openings, is fitted within the mouth of a vehicle airbag (not shown) which is sealed around said upper part of the housing.

One gas bottle 2 contains a fuel in the form of a combustible gas such as, for example, hydrogen, methane, ethane, propane or butane, or a mixture of one or more such gases. The fuel may be provided in a pure form or in admixture or mixed with an inert gas such as nitrogen, argon, helium or carbon dioxide. The pressure of gas within the bottle may be such that the gas is in partly liquefied form. The other gas bottle 4 contains an oxidising gas such as air, oxygen or nitro-oxide. The oxidising gas may be again mixed with an inert gas such as nitrogen, argon, helium, carbon dioxide or mixtures thereof. Again the pressure may be such that the gas is partially liquefied.

As best shown in Figures 3 and 4, formed in the central part of the end wall 10 of each bottle, 2, 4, is a respective outlet opening 18, the opening 18 being sealed by means of a respective metal foil 20 extending across the opening 18 on the outer face of the respective wall 10 and adhesively secured to that outer face. A squib 22 is mounted in a squib housing 24 carried by the central housing 12 and located between the opposing parallel end walls 10 of the gas bottles 2, 4. The squib housing 24 is in the form of a cylinder 26 with an axial bore accommodating a complementary piston 28. The upper part of the squib housing 24 supports a bracket which has two integral planar arms which are parallel with and lie against respective end walls 10 of the bottles 2 and 4 and extend across the respective sealing foils 20. The arms 30 are each provided with a respective line of mechanical weakness 32 at a position where the arm is connected to the bracket on the squib housing. The squib housing 24 and the arms 30 may be formed as an integral plastic or metallic moulding.

The piston 28 is provided with a piston head 28a received within the circular cross-section bore of cylinder 26. The piston includes a piston rod 34 which extends from the piston head 28a, along the axis of said bore or cylinder 26, between the two arms 30. The piston rod 34 carries outwardly directed support flanges 36 which, in the initial position of the components illustrated in Figure 3, directly engage the free ends of the respective arms 30.

In this position, the arms 30 act as support members to support the foils 20 and are in turn supported by the support flanges 36. Piston head 28a and piston rod 34 might be made in one piece When the airbag is to be inflated, the squib 22 will be fired. Gas generated by the squib will apply a force to piston head 28a moving the piston 28 axially, along the cylinder 26. The piston thus moves to a position, shown in Figure 4, in which the outwardly directed flanges 36 are moved past the free ends of the arms 30 so that the arms 30 are no longer supported at their free ends. This enables the arms 30 to pivot inwardly, about the lines of mechanical weakness 32, so that the arms 30 no longer provide support for the foils 20, enabling the foils to be ruptured by gas pressure within the gas bottles 2 and 4. Gas from the gas bottles 2 and 4 will thus flow through the openings 18, past the outwardly directed flanges 36 and out through the gas flow apertures in the tubular part 16 into the interior of the airbag. As the gases flow, so will the gases be mixed.

The means for sealing the gas bottles and the mechanism for rapidly breaking the seals in an emergency situation is a modification of that disclosed in GB2417066. In the embodiments of the present invention described and shown in the drawings, the pyrotechnic squib used to propel the piston into a position in which it no longer supports the arms 30 which in turn support the foils 20, is also used to ignite the gases from the gas bottles 2, 4.

As noted below, the igniter tube/piston rod 34 has features to ensure a reliable and rapid ignition of the gases issuing from the gas bottles 2, 4 despite the high flow rate and high turbulence of these gases.

The primary modification as compared with the arrangement of GB2417066, in the embodiments of Figures 1 to 4, is that the piston rod forms an igniter tube through which the hot gases produced by the firing of the squib are directed. In the embodiments of Figures 1 to 4, the piston rod 34 has a longitudinal bore 40 therethrough whilst the piston head 28a has an axial bore 42 therethrough of diameter smaller than that of the igniter tube and smaller than that of the cylinder bore 26 in which the piston head moves. Accordingly, when the squib is ignited, the restricted size of the axial bore through the piston head is small enough to allow sufficient pressure of gases from the squib to build up behind the piston head 28a to force the piston along its cylinder and thus to move the support flanges 36 extending from the piston rod/igniter tube 34 past the free ends of the arms 36 so that the foil seals 20 are no longer supported and are thereby ruptured by the pressure of the gases within the gas bottles. The bore 42 may be as long as the entire length of the piston rod/igniter tube 34.

As shown, the igniter tube is arranged with its axis extending through the opening (not shown) of the airbag (not shown) connected with the inflator and with its free end facing towards the interior of the bag, ideally, as illustrated, being coaxial with the conduit part 16 of the housing 12. The hot gases from the firing of the squib 22 pass through the bore 42 to the end of the tube 34 adjacent the piston head so that they pass at high speed along the bore 40 of the tube to emerge from the open end of the tube 34 remote from the piston head. It is possible (but not necessary) to design the piston so that at least one port or hole 46 is formed through the wall of the tube, such as to be disposed in the region within the chamber 14 into which the gases from the gas bottles are discharged from these bottles. In operation, the hot gases from the squib, passing along the bore 40 of the tube at high velocity, draw in, by the Venturi effect or by pressure difference between mixing chamber 14 and housing part 16, gases from around the tube 34, so that the gases thus drawn into the tube start burning within the tube to produce an enhanced flame from the free end of the tube, to ensure rapid combustion of the remaining gases discharged from the gas bottles, and rapid and reliable inflation of the gas bag. The preliminary burning of the bottle gases within the tube also creates free radicals which also encourages combustion of the gases outside the igniter tube.

In the arrangement shown in Figures 1, 3 and 4, the conduit part 16 of the housing terminates in a Continuous end waIl 17, the end of the igniter tube 34 remote from the piston head, in the projected position of the piston illustrated in Figure 4, opening into the conduit in the region behind said end wall, at the level of the apertures in the peripheral wall of the conduit. It will be noted in Figure 4 that, in this position, the support flanges 36 engage an abutment provided by an inner end of the tubular part 16 of the housing 12 to limit movement of the piston towards said end wall 17. In the variant arrangement shown in Figure 2, the end wall 17 of the conduit 16 has a central aperture in which is fitted a tubular insert 50 providing a through-passage terminating in an outlet or nozzle, beyond the conduit and wall 17 and thus within the inflatable bag (not shown). The opposite end of the through passage in said insert 50 is adapted to receive the free end of the igniter tube 34 in the projected position of the piston (shown in Figure 2) so that the burning gases propelled along the igniter tube discharge, not into the conduit, but, after passing through the passage in the insert 50, discharge directly into the inflatable bag. The flanges 36, bracket with arms 30 and foils are omitted in Figures 1 and 2 for ease of illustration only.

The igniter tube or piston rod 34 may be shaped internally and externally to secure a desired degree of suction of the gas mixture, e.g. to enhance the Venturi effect and/or to enhance ignition performance, or to ensure good flame holding. The tube 34 may have reductions in flow cross-section at specific locations to control pressure pulses from the squib.

Referring to Figures 5 and 6, in which parts corresponding to parts in Figures 1 to 4 have corresponding references in a further variant, the longitudinal axis of the housing part 16 providing the conduit which fits into the air bag is at right-angles to the longitudinal axis of the squib housing 24, i.e. of the cylinder 26 in which the piston 28 is located, It will be understood that the plane of section of figures 5 and 6 is at right angles to the longitudinal axes of the gas bottles and substantially mid-way between the latter so that the gas bottles are not visible in Figures 5 and 6. In the embodiment of Figures 5 and 6, the piston 28 is solid. However, a transverse bore 54 through the wall of the cylinder 26 provided by the squib housing 24, at a location adjacent the end of that cylinder remote from the squib 22, is axially aligned with the housing part 16 providing the conduit referred to. In the inactivated condition of the unit illustrated in Figure 5, the transverse bore 54 is sealed off by the part of the piston 28 within the cylinder, but is disclosed when the piston is projected to the position shown in Figure 6, (releasing the arms 30 and hence unseating the gas bottles), thus allowing hot gases produced by the burning of the squib to exit through the bore 54 to ignite the mixture of the gases from the bottles. It wilt be noted that, in this projected position of the piston 28, the free end of the piston outside the cylinder 24 engages and is arrested by the wall of the housing 17. Preferably an igniter tube corresponding in form to the piston rod/igniter tube of Figures 1 to 4, but without the support flanges 36, may be fitted in the bore 54 to extend into the conduit within tubular part 16, and may either terminate within the conduit or may extend through an aperture (not shown) in the end waIl 17 of the conduit, into the airbag itself.

Whilst, in the embodiments illustrated, the igniter tube has been incorporated in the squib arrangement used to break the gas bottle seals, it will be understood that an igniter tube of the same configuration as illustrated may be used with an independent igniter squib. In this case, an item corresponding in form to the piston head, but fixed within the squib housing may be interposed between the squib and the tube 34 with port 46, to produce a narrow high speed jet of squib gases (through bore 42) along the axis of the tube 34. The tube 34 in this case will again extend into the chamber 14 with the squib housing being again mounted in the central housing 12 for example.

However it is preferred to use the same squib to unseal the gas bottles and to ignite the gases, to keep construction simple and reliable and to keep costs down.

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.

Claims (9)

1. An inflator for an airbag, comprising a bottle (2) containing a pressurised oxidisable gas and a bottle (4) containing a pressurised oxidising gas, the bottles being connected with a structure (12) providing a mixing chamber (14), the bottles having respective discharge openings (18) sealed by respective sealing means (20) sealing off the interiors of said bottles from said chamber (14), the inflator including opening means (22, 28, 30), which can be activated to cause or allow the seals provided by said sealing means (20) to be broken to allow the gases from said bottles to pass into said chamber (14) and thence via an opening to exit into such airbag, characterjsed in that opening means (22, 28, 30) includes an igniter comprising a pyrotechnic squib (22) confined in structure including an igniter tube (34) extending within said chamber (14) and arranged so that when said seals (20) are broken and the squib (22) is ignited, burning gases from the squib will be discharged through said tube (34) to ignite the mixture of gases discharged from said bottles.

2. An inflator according to Claim 1 wherein said tube 34 is arranged to release ignition gases at a position that is favourable for a reliable ignition, such as in a position of a preferred gas flow, mixing, turbulence and pressure.

3. An inflator according to Claim 1, wherein said tube (344) includes one or more ports or holes (46) in the wall thereof through which such gas mixture can be drawn into the tube by the flow of igniter squib gases therealong, to commence combustion of such gases from said bottles during transport of these gases along the igniter tube.

4. An inflator according to Claim 1, wherein said means for causing or allowing the seals provided by said sealing means to be broken to allow the gases from said bottles to pass into said chamber includes a piston (28) moveable along a complementary cylinder (26) by pressure of gases generated by said squib when the latter is ignited.

3. 5 5. An inflator according to Claim 4 wherein said tube (34) is carried by said piston (28) and a restricted passage (42), restricted in cross-section as compared with the cross-section of said cylinder (26), is provided through said piston (28) and communicates with the interior of said tube (34) for conveying burning gases from the squib through the piston to said tube. 4. 10

5.

6. An inflator according to Claim 4 wherein said tube is carried by said complementary cylinder (26) and the bore of said tube communicates with the interior of said cylinder (26) via a transverse passage (54) in the wall of said cylinder (26), at a location such as to be blocked by said piston (28) in the normal unactivated state of said means for causing or allowing the seals provided by said sealing means (20) to be broken, but such as to be disclosed by movement of said piston (28) when the squib (22) is fired, to allow burning gases from the squib to be discharged through said tube to ignite the mixture of gases discharged from said bottles.

7. An inflator for an airbag, comprising a bottle (2) containing a pressurised oxidisable gas and a bottle (4) containing a pressurised oxidising gas, the bottles being connected with a structure (12) providing a chamber (14) including a conduit (16) for connection with a vehicle airbag, the bottles having respective discharge openings (18) sealed by respective sealing means (20) sealing off the interiors of said bottles from said chamber (14), the inflator including means (22, 28, 30) which can be activated to cause or allow the seals provided by said sealing means (20) to be broken to allow the gases from said bottles to pass into said chamber (14) and thence via said conduit (16) into such airbag, said means including a pyrotechnic squib (22) mounted in a housing including a cylinder (26) receiving a piston (28) moveable along the cylinder by pressure of gases generated by said squib when the latter is ignited and arranged by such movement to cause or allow said seals (20) to be broken, characterised in that a transverse passage (54) is provided through the wall of said cylinder (26) at a location such as to be blocked by said piston (28) in the normal unactivated state of the inflator, but such as to be disclosed by movement of said piston when the squib is fired, to allow burning gases from the squib to be discharged through said tube to ignite the mixture of gases discharged from said bottles.

8. An inflator according to any of Claims 4 to 7 wherein each gas bottle is sealed by a rupturable foil (20), said means which can be activated to cause or allow said seals to be broken including respective support members (30) engaging the rupturable foils to maintain the rupturable foils in an Un-ruptured state, each said support member (30) being retained in position by a part (36) carried by said piston (28) which part directly engages the support member, the arrangement being such that movement of the piston (28) along said cylinder (26) as a result of firing the squib (22) thereby moves said part (36) carried by said piston past said support members (30), permitting the support members to move to positions in which the foils (20) will rupture to permit gas to escape from the gas bottles.

9. An air-bag system provided with an inflator according to any of Claims 1 to 8.