GB2306214A

GB2306214A - A vehicle air bag system

Info

Publication number: GB2306214A
Application number: GB9521140A
Authority: GB
Inventors: Anthony Pike
Original assignee: AIRBAG PROTECTION SYSTEMS Ltd
Current assignee: AIRBAG PROTECTION SYSTEMS Ltd
Priority date: 1994-12-20
Filing date: 1995-10-16
Publication date: 1997-04-30
Also published as: GB9521140D0

Abstract

A vehicle air bag system in which a sealed (21) pressurised gas cylinder (20) is connected to chamber (24) by a cylinder seal opener (30) so that gas from the cylinder flows into the chamber, and exit of which is closed by a frangible seal (36). The frangible seal is broken by means of an explosively operated actuator (44) when an air bag (70) is required to be filled. This enables the air bag to be inflated very rapidly from the gas cylinder via the chamber. The cylinder is preferably filled with an inert gas such as argon.

Description

A Vehicle Air Baa System This invention relates to a vehicle air bag system having a rapid release device.

It is known from GB Patent No. 1 323 273 to provide a rapid release device for opening a pressurised gas container suitable for inflating an air bag. The release device is an explosively actuated piston which punches a hole in the cylinder from within. The escaping gas then enters a distribution chamber which extends and through ports in the chamber fills the air bar with the escaping gas in a supposed 15 to 40 msec. A problem with this arrangement is that the cylinder cannot be pressurised without the release device being removed. To refit the release device under pressure would require a complicated and expensive arrangement. Furthermore the piston would be unlikely to open the cylinder quickly enough to meet presently required air bag inflation times due to the piston partially blocking the punched hole.

To overcome those problems GB 1 334 324 proposes to break a seal in a cylinder outlet from outside the cylinder by a small explosive device in the outlet. Again there is a problem with ensuring a sufficiently wide opening to release the gas into the air bag in the short time required.

Other air bag inflation systems are known which use a pyrotechnic generated gas. This gas in this system tends to be about 20000C so that the air bag has to resist this temperature initially. There are clearly problems with such high temperatures one of which is the heating up the bag itself which may be too hot for people in a vehicle fitted with such a system.

According to the present invention there is provided a vehicle air bag system having a rapid release air bag inflation device and an air bag to be inflated by the device, the device comprising a pressurised gas cylinder having a cylinder seal arranged to seal the cylinder before assembly, a chamber having an entry and an exit, cylinder seal opening means enabling gas from the cylinder to enter the chamber through the entry on assembly, a frangible seal closing the exit, an explosively operable frangible seal breaking means enabling gas from the chamber to pass through the exit to the air bag.

The provision of the cylinder seal opening means enables the device to be assembled with an already pressurised cylinder. The chamber with a sufficiently large exit allows a very rapid passage of gas from the chamber to the air bag: the provision of a frangible seal rather than a fractured or pierced seal or a break stem seal allows also enables very rapid inflation of the air bag so that under trial conditions inflation has been achieved in 15 milliseconds which is well within the minimum design requirement for 20 milliseconds. In that respect it is doubted that the device of GB 1 323 273 would ever have achieved its lower limit of 15 milliseconds because of the restriction of the cylinder punching arrangement. Perhaps that is why the upper limit of 40 milliseconds is given for that proposal.

Preferably the gas cylinder is filled with argon which is advantageous in having fire retardant properties and which has a heavier enough molecular weight to avoid leakage in the system. In this respect helium has caused leakage problems. The cylinder is preferably of a volume and at a pressure to supply 8 to 20 litres of gas at a pressure of about 0.4 bar.

The frangible seal is preferably formed of a ceramic material which breaks up rapidly when struck by the explosive seal breaking means. In order to improve its sealing capability the ceramic material may be coated with a sealant composition.

The frangible seal is preferably backed with a pressure resisting part of the device to leave a circular unsupported central area of the frangible seal of about 4/10 of the total surface area of the frangible seal. This ensures that the seal breaks up into particle sizes which do not block the gas passages between the chamber and air bag. Preferably a screen having a mesh size of between 1 and 2 mm square and suitably 1.5 mm square to trap seal particles. Under trial, particle sizes mostly varied between 2 and 2.5 mm across. Preferably the frangible seal is between 15 and 20 mm in diameter and suitably about 16 mm in diameter whilst being between 2.5 and 4 mm and suitably about 3 mm thick.

The air bag may be a "skeletal air bag" of the kind where gas filled tubes support an ambient air introduced and filled bag or else a more conventional pressurised gas filled bag. The use of a skeletal bag requires less gas to inflate than the conventional totally gas filled bag so is preferred in order to keep the size of the pressurised gas cylinder to a minimum. This is an important factor when designing side impact air bag systems. One such skeletal air bag is shown in US Patent No. 3 888 505.

Preferably pressure monitoring means are connected to the chamber between cylinder and air bag so as to detect any fall off of pressure in the chamber which would cause the system to fail. A minimum preferred chamber pressure before breaking the frangible seal is 200 bars. The chamber pressure is preferably at between 210 and 220 bars on assembly with the pressurised gas cylinder where the gas cylinder before assembly is between 240 and 260 bars and suitably 250 bars.

The explosively operable breaking means is suitably a known explosive actuator mounted so that its actuation axis is perpendicular to the major pressure resisting surface of the frangible seal with gas exiting from the chamber around the actuator.

In one embodiment a gas distribution area is provided downstream of the chamber to collect gas from the chamber exit and channel it to the air bag. The distribution area has a plurality of distribution outlets located radially away from the axial centre of the area so that particles exiting axially from the chamber around the breaking means may be to at least some extent prevented from being shot into the distribution outlets. In the case of use with a skeletal air bag, each distribution outlet can be connected directly to the supporting tubes.

According to a further aspect of the invention there is provided an air bag system comprising a pressurisable gas cylinder, the cylinder being connected to a chamber having an outlet sealed by a frangible ceramic seal, explosive means for breaking said seal, means for distributing gas escaping from said chamber connected to an air bag and an inertia sensitive device arranged to cause an electric current to the explosive means to cause the explosive means to fire and break said seal.

Inertia sensitive devices for air bags are well known. The use of a ceramic frangible seal preferably in the form of a disc is particularly advantageous in ensuring that the chamber outlet is very rapidly opened within the minimum design requirement to inflate an air bag within 20 milliseconds.

Whilst frangible seals made from ceramic material are known at least from GB Patent No. 1 334 324 which discloses an air bag system, the provision of the seal at the exit of a chamber downstream of the cylinder enables a larger seal to be provided than that deducible from GB Patent No. 1 334 324 where the seal is in the neck of the cylinder . Here a more rapid flow of gas from the cylinder is possible.

This is important where bag inflation time is crucial to save injury to vehicle occupants.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross section of a rapid release air bag inflation device and diagrammatically other parts of the system according to the invention, and Figure 2 is a conceptual elevation of a skeletal air bag which may form part of the system of Fig. 1.

In Figure 1 there is shown a pressurised cylinder 20 and a chamber body 22, the body enclosing a chamber 24 having an entry 26 and exit 28.

Prior to assembly of the cylinder 20 and the body 22 together, the 100 millilitre cylinder is filled with about 30 litres of argon at atmospheric pressure and compressed to 250 bars. The cylinder is then sealed with a seal 21.

On assembly the cylinder is screwed into threaded end portion 27 of the body until the seal impinges on a hollow seal opening member 30 mounted in the entry 26. Further screwing of the cylinder into the body pierces the seal as shown and the cylinder then seats on '0' ring 32. A suitable sealant may be applied to the thread of the neck 23 of the cylinder. The opening member 30 is sealed by its flange 32 by an '0' ring 33 into the entry 26. The pressure within the cylinder is then released into the chamber having a volume of about 8 cc so that the pressure in the cylinder and chamber then reduces to about 217 bars.

The exit 28 of the chamber is sealed by means of a cylindrical ceramic disc 36 which is 16 mm in diameter and 3 mm thick. The disc 36 seats inwardly onto '0' ring 38 and is backed downstream by ring plate 40 which has an internal opening diameter of 10 mm. A threaded collar 42 then clamps the ring plate onto the ceramic disc to tighten the disc onto '0' ring 38. This leaves about 4/10 of the surface area of the disc unsupported at its centre.

The disc 36 is made of known ceramic material but is coated with a sealant such as "Torr-seal" made by the Varian Company which has been found necessary to prevent leakage under high pressure.

The collar 42 carries at its centre an explosive actuator 44 suitably an ICI Nobel "Metron" actuator No. DR 2001 which has a piston 46 which when an electrical current is passed through leads 48 fires into disc 36 to break up the disc and unseal the chamber 24. Around the actuator and leading from the downstream side of disc 36 to distribution chamber 50 are ports 52 at the downstream end of which is a mesh screen 54 having a mesh size of 1.5 mm square. This is designed to catch disc particles normally about 2-2.5 mm across when the disc is broken.

The distribution chamber 50 has eight or ten distribution ports 64 arranged radially around the inner circumference of plate 62 (only four such ports are indicated in the drawings for clarity). Each port 64 has a cylindrical extension 66 which receives the turned over end 68 of air bag inflation tubes 60 (only one is shown for clarity) for air bag 70 indicated in broken lines and which will be described below. The ends 68 of tubes 60 are formed over inwardly extending cylindrical tubes 72 which extend from outer plate 74 which is screwed to plate 62 by screws 76.

At the mid point of chamber 24 a radially extending port 80 provides a passage to pressure monitoring device 82 which comprises a normally closed spring contact pressure switch which opens when chamber pressure falls below 200 bars to cause a red indicator light to indicate an unacceptably low pressure.

A known inertia device 90 is provided to provide an electrical firing current via leads 48 to actuator 44.

A skeletal air bag will now be described which is preferred to a conventional air bag. However a conventional air bag can be fitted by a suitable adaptor to plate 62. This leaves ports 64 in the same position indicated above.

The skeletal air bag 70 comprises an impermeable bag 92 attached to plate 93 within which are a plurality of resilient tubes 60 corresponding to and connected upstream to ports 64 at the downstream end of which are small holes 97 from 1 mm to 5 mm in diameter through which gas can escape but is restricted. At the top (as shown) of the bag is a circular resilient flap valve plate 94 for closing large holes 95 in top plate 96.

In operation gas is let into tubes 60 which spring up under the gas pressure raising top plate 96. As plate 96 rises so ambient air is drawn into bag 92 through holes 95 as indicated by arrows B. When tubes 60 are extended and quite rigid under pressure valves resilient plate 94 seals holes 95 so that air bag 70 can contain about 60 litres of air. The tubes 60 contain about 12 litres of argon.

Overpressure in tubes 60 is allowed to escape through small holes 97.

Claims

C L A 1 M S

1. A vehicle air bag system having a rapid release air bag inflation device and an air bag to be inflated by the device, the device comprising a pressurised gas cylinder having a cylinder seal arranged to seal the cylinder before assembly, a chamber having an entry and an exit, the cylinder seal opening means enabling gas from the cylinder to enter the chamber through the entry on assembly a frangible seal closing the exit, an explosively operable frangible seal breaking means enabling gas from the chamber to pass through the exit to the air bag.

2. A system according to claim 1 wherein the frangible seal is formed of a ceramic material.

3. A vehicle air bag system comprising a pressurisable gas cylinder, the cylinder being connected to a chamber having an outlet sealed by a frangible ceramic seal, explosive means for breaking said seal, means for distributing gas escaping from said chamber connected to an air bag and an inertia sensitive device arranged to cause an electric current to the explosive means to cause the explosive means to fire and break said seal.

system as claimed in any one of claims L to o 3 wherein the cylinder is pressurised with an inert gas.

system as claimed in claim 4 wherein the inert gas is at least mainly argon.

6. A system as claimed in any one of claims 1 to 5 wherein the frangible seal is coated with a sealant.

7. A system as claimed in any one of claims l to 6 wherein a screen is located downstream of the frangible seal between the seal and air bag.

8. A system as claimed in claim 7 wherein the screen has a mesh size between 1 mm and 2 mm and preferably about 1 .5 mm.

9. A system as claimed in any one of claims 1 to 8 wherein the air bag is formed as a skeletal dir bag of the kind where a gas fillable space or spaces extends the bag on release of gas from the chamber connected to the cylinder, the bag having at least one non-return valve through which ambient air is introduced to fill the bag on extension by the spaces.

U. A system as claimed in claim 9 wherein the gas fillable space(s) is/are provided with at least one vent.

11. A system as claimed in claim 9 or 10 wherein the gas fillable space(s) ls/are a plurality of tubes.

12. R system as claimed in any one of claims 1 tn 11 wherein a pressure monitoring means is connected tc, tfie chamber.

13. A system as claimed in any one of claims 1 to 12 wherein the pressure in the chamber is maintained at a pressure of at least 200 bars and preferably up to 220 bars.

14. A system as claimed in any one of claims 1 t-o 13 wherein the frangible seal is backed with a pressure resisting part of the device to leave an unsupported central area of the frangible seal of between a half and 3/10 and preferably about 4/10 of the total surface area of the pressure resisting face of the frangible seal.

15. A system as claimed in claim 1 or 2 wherein the cylinder opening means comprises a hollow tube having c0 sharp seal piercing end.

16. A system as claimed in claim 15 wherein the hollow tube as formed with a piercing end having a piercing surface angled at an acute angle relative to the axis of the tube so that when the seal is rotated relative to the tube on assembly a minor part of the seal remains uncut.

17. A vehicle air bag system having a rapid release air bag inflation device substantially as described with reference to Figure 1 of the accompanying drawings.

L8. A vehicle air bag system having an inflatable air bag substantially as described with reference to Figure 2 t)f the accompanying drawings.

Amendments to the claims have been filed as follows 1. A vehicle air bag system having a rapid release air bag inflation device and an air bag to be inflated by the device, the device comprising a pressurised gas cylinder having a cylinder seal arranged to seal the cylinder before assembly, a chamber having an entry and an exit, the cylinder seal opening means enabling gas from the cylinder to enter the chamber through the entry on assembly a frangible seal closing the exit, an explosively operable frangible seal breaking means enabling gas from the chamber to pass through the exit to the air bag, wherein the air bag is formed as a skeletal air bag of the kind where a gas fillable space or spaces extends the bag on release of gas from the chamber connected to the cylinder, the bag having at least one non-return valve through which ambient air is introduced to fill the bag on extension by the spaces.

2. A system according to claim 1 wherein the frangible seal is formed of a ceramic material.

3. A vehicle air bag system comprising a pressurisable gas cylinder, the cylinder being connected to a chamber having an outlet sealed by a frangible ceramic seal, explosive means for breaking said seal, means for distributing gas escaping from said chamber connected to an air bag and an inertia sensitive device arranged to cause an electric current to the explosive means to cause the explosive means to fire and break said seal.

4. A system as claimed in any one of claims 1 to 3 wherein the cylinder is pressurised with an inert gas.

5. A system as claimed in claim 4 wherein the inert gas is at least mainly argon.

6. A system as claimed in any one of claims 1 to 5 herein the frangible seal is coated with a sealant.

7. A system as claimed in any one of claims 1 to 6 wherein a screen is located downstream of the frangible seal between the seal and air bag.

8. A system as claimed in claim 7 wherein the screen has a mesh size between 1 mm and 2 mm and preferably about 1.5 mm.

9. A system as claimed in claim 8 wherein the gas fillable space(s) is/are provided with at least one vent.

10. A system as claimed in claim 8 or 9 wherein the gas fillable space(s) is/are a plurality of tubes.

11. A system as claimed in any one of claims 1 to 10 wherein a pressure monitoring means is connected to the chamber.

12. A system as claimed in any one of claims 1 to 11 wherein the pressure in the chamber is maintained at a pressure of at least 200 bars and preferably up to 220 bars.

13. A system as claimed in any one of claims 1 to 12 wherein the frangible seal is backed with a pressure resisting part of the device to leave an unsupported central area of the frangible seal of between a half and 3/10 and preferably about 4/10 of the total surface area of the pressure resisting face of the frangible seal.

14. A system as claimed in claim 1 or 2 wherein the cylinder opening means comprises a hollow tube having a sharp seal piercing end.

15. A system as claimed in claim 14 wherein the hollow tube as formed with a piercing end having a piercing surface angled at an acute angle relative to the axis of the tube so that when the seal is rotated relative to the tube on assembly a minor part of the seal remains uncut.

16. A vehicle air bag system having a rapid release air bag inflation device substantially as described with reference to Figure 1 of the accompanying drawings.

17. A vehicle air bag system having an inflatable air bag substantially as described with reference to Figure 2 of the accompanying drawings.