GB2281226A - An air bag unit - Google Patents

Abstract

In a gas generator a first vessel (1) having a side wall, and an end closure (2) contains a mixture of helium and oxygen under high pressure of approximately 200 bar and a second vessel (21) contains hydrogen at a pressure of approximately 30 bar. A triggering mechanism is provided which, when activated, enables gas from both vessels to flow to a catalytic combustion zone (25). The combustion zone and flow-path to the airbag inlet is of non-decreasing cross-sectional area. In the preferred embodiment the combustion zone (25) is of annular form at the outlet of the annular outer periphery of the chamber. Thus the outlet is at the region of greatest cross-sectional area. As the gases combust there is no restriction and consequently no pressure rise during combustion obviating any risk of explosion. <IMAGE>

Description

DESCRIPTION OF INVENTION "IMPROVENENTS IN OR RELATING TO AN AIR BAG UNIT" THE PRESENT INVENTION relates to an air bag unit for use in inflating an air-bag in a motor vehicle.

Various types of gas generator have been proposed for use in inflating an air-bag in a motor vehicle in the event that an accident arises. It is important that the air-bag is inflated within a very brief period of time following the sensing of an accident. Consequently, it has been proposed to use various pyrotechnic materials in gas generators. Pyrotechnic materials are inherently dangerous, since a typical pyrotechnic material is "selfcombusting". In other words the material contains all the chemicals necessary for combustion to occur, and once combustion has been initiated, then that combustion will, in a very short period of time, be fully completed.

The present invention relates to an air bag unit having gas generator which is capable of generating gas very swiftly, but which does not use a pyrotechnic material as the primary source of gas.

According to this invention there is provided an air bag unit comprising an air bag having an inlet and a gas generator having a gas outlet connected to said inlet by a flow path, the gas generator comprising a first vessel containing a first gas and a second vessel containing a second gas, one of the gases containing oxygen and the other of the gases containing a gas adapted to combust with oxygen, the gas generator comprising means to direct the two gases to a combustion zone where the gases combust when the gas generator is activated, the combustion zone having an outlet which comprises the gas outlet of the gas generator, the combustion zone having a non-decreasing cross-sectional area from the interior of the combustion chamber to the outlet, said flow path having a cross-sectional area which is, at each point on the flow path, at least equal to the cross-section of the outlet of the combustion zone.

Preferably the combustion zone is of increasing cross-sectional area.

Conveniently the combustion zone is of annular form, having an annular outlet at the outer periphery of the combustion chamber.

Advantageously one vessel is provided with at least one outlet port, the or each outlet port comprising an aperture sealed by sealing means, there being a piston located adjacent and in supporting relationship with the sealing means adapted to support the sealing means, means being provided to move the piston, when the gas generator is to be activated, to a position in which the piston no longer supports the sealing means, the pressure within the vessel breaking the sealing means or otherwise opening the aperture sealed by the sealing means, thus establishing a flow path to the combustion zone for gas in that vessel.

Conveniently the part of the vessel that defines the sealed aperture or apertures is in the form of a reentrant well, the piston being mounted for sliding of example, with reference to the accompanying drawings in which FIGURE 1 is a cross-sectional view of the operative parts of an air bag unit in accordance with the invention, and FIGURE 2 is a corresponding view showing the gas generator of the air bag unit of Figure 1 in use.

Referring initially to Figure 1, an air bag unit has a gas generator which comprises a first gascontaining gas bottle 1 of cylindrical form having one end closed by a closure plate 2 which is welded 3 or otherwise secured to the housing 1 of the gas bottle.

The closure plate 2 is of circular form, but defines a central inwardly directed well 4, which is of circular cross-section. The well 4 effectively forms a cylindrical side wall 5 which is co-axial with the housing 1 but of a lesser radius, and also defines an end wall 6 forming the bottom of the well.

A plurality of apertures 7 are provided in the side wall 5 at equi-spaced positions, but only one aperture is shown in Figure 1. The aperture is initially sealed by means of a sealing disc 8 formed of a relatively thin, but gas-tight material, such as aluminium foil, which may be soldered or welded in position.

A plurality of air passages 9 are defined projections 10 provided at the open end of a tubular flame-guide element 12. The projections 12 are provided at the end of a portion 13 of a first diameter. The tubular element has an enlarged end 14 remote from the movement on a tubular member extending into the well, there being a flow path between the interior of the tubular member and the end face of the piston, the piston being a substantial sliding sealing fit within the well, there being a gas generating squib provided to supply gas to the tubular member.

Advantageously the squib is mounted within an end portion of the tubular member.

Conveniently the second vessel is mounted in position to surround part of the tubular member that projects from the re-entrant well.

Preferably the piston is provided with a peripheral skirt having a plurality of transverse bores therethrough, the piston being adapted to deflect an end wall of the second vessel, thus opening a fluid flow path between the deflected end wall of the second vessel and part of the tubular member on which the second vessel is mounted, that flow path continuing through the transverse bores provided in the skirt of the piston to the combustion zone.

Advantageously the first vessel contains a mixture of inert gas and oxygen at a pressure of approximately 200 bar, and the second vessel contains hydrogen at a pressure of approximately 30 bar.

Conveniently the inert gas is helium.

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 portion 13, that enlarged end 14 containing an ignition squib 15.

A piston 16 is provided, mounted for sliding movement along the lesser diameter portion 13 of the tubular element 12. The piston is a sliding substantially sealing fit within the well. The piston 16 has an initial position within the well 4. When in this position a side wall 17 of the piston is located adjacent the foil element 8 sealing the aperture 7. The piston thus supports the foil element 8.

The piston has a rearwardly directed skirt 18 provided with a plurality of small diameter transverse bores 19 which form a flow path from a space 20 which is located on the interior of the skirt 18 of the piston, to the outer wall 17 of the piston.

Mounted on the enlarged diameter portion 14 of the tubular element 12 is a second gas-containing housing comprising a cylindrical side wall 21 carrying a first inwardly directed end wall 22 which is securely connected to the end of the enlarged diameter portion 14 of the tubular element 12 and a second inwardly directed end wall 23 which contacts the exterior of the enlarged diameter portion 14 of the tubular element 12 in a sealing manner.

Mounted on the part of the end cap 2 adjacent the housing 1 and also mounted on the end wall 23 of the second gas-containing housing are a plurality of elements 24 of a catalyst such as a catalytic inert metal. The elements may comprise blocks of platinum metal or other similar catalyst such as osmium, iridium, palladium, rhodium and ruthenium.

The metal catalyst may be mounted on a suitable porous substrate such as alumina, asbestos or a silicate.

The first gas-containing gas bottle 1, contains a mixture of inert gas, such as helium and oxygen at a pressure of 200 bar. The quantity of helium may be adjusted between 0% and 50% of the total mixture. Thus, the gas bottle may contain pure oxygen.

The gas presses the sealing disc 8 against the side wall 17 of the piston. The piston supports the sealing disc 8. The disc 8 thus seals the aperture 7.

The second gas bottle, defined by the side wall 21 and the end walls 22,23 contains hydrogen at a pressure of 30 bar. Inert gas may, if desired, be combined with the hydrogen.

The space 25 between the end cap 2 and the end wall 23 forms a combustion zone. The outlet 26 of the combustion zone is an annular outlet located at the periphery of the space 25, in alignment with the cylindrical wall gas-containing housing 1 and the cylindrical wall 21 of the second gas-containing bottle.

It is thus to be appreciated that the combustion space 25 is effectively of increasing cross-sectional area from its interior, adjacent the tubular member 12, to its termination or outlet, i.e. the annular outlet 26 in alignment with the side wall of the gas bottle 1 and the side wall 21.

In operation of the gas generator as described, initially the squib 15 is ignited in response to a signal from an accident sensor. Gas generated from the squib passes down the tubular element 12, through the air spaces 9 inbetween the projections 10 and the air thus engages the end face of the piston 16. The piston 16 is thus driven to move towards the left as shown in Figure 1, the piston thus reaching the position shown in Figure 2. The movement of the piston has two effects.

Firstly, the side wall 17 of the piston 16 no longer supports the sealing disc 8 present in the aperture 7. The sealing disc 8 is thus subjected to a pressure of approximately 200 bars from the gas contained within the first gas bottle, but is no longer supported by the outer wall 17 of the piston 16. Whilst the sealing disc 8 was able to withstand the applied pressure when supported by the side wall 17 of the piston 16, when no longer supported the sealing disc ruptures thus permitting the helium and oxygen mixture to flow, as indicated by the arrow 27, from the interior of the gas bottle, through the aperture 7, past the tubular member 12, past the piston 16 and into the combustion chamber 25.

Secondly, the movement of the piston causes the skirt 18 of the piston to engage and deflect inwardly the end wall 23 of the gas bottle containing hydrogen. This opens a flow path between the end of the wall 23 and the exterior of the enlarged diameter portion 14 of the tubular member 12 for the hydrogen gas from within the second gas bottle. The hydrogen gas flows within the skirt 18 of the piston 16 and then flows through the radially extending bores 19 into the combustion space 25, as indicated by arrow 28. The hydrogen is thus there mixed with the helium and oxygen gas. The resultant mixture is ignited by the catalyst elements 24.

Because the combustion space 25 continually diverges towards its outlet 26 or, in other words, continually has an increasing cross-section as the gas advances towards the outlet 26, there is no restriction on the outlet, and thus the combusting gas is continually permitted to diverge and expand, obviating any risk of an explosion occurring.

The gas bottle, as described above, is mounted within the lower part of a housing 29. The end wall 22 of the second gas bottle is connected to a side wall 30 of the housing 29. An aperture 31 present in the side wall provides communication with the squib 15.

The outlet 26 of the combustion chamber communicates with an annular space 31 which surrounds the first gas bottle 1 and the side wall 21 of the second gas bottle.

A baffle 32 having apertures 33 bounds part of the annular space 31 and separates that space from a chamber 34 which contains a folded air bag 35. The chamber 34 is closed by a cover 36 which retains the folded air bag 35 in position. The cover 36 is connected to the housing 29.

The apertures 33 in the baffle 32 effectively form an inlet for the air bag.

It is to be noted that a flow path exists through the annular space 31 from the outlet 26 of the combustion space 25, to the baffle 32 and thus through the apertures 33 in the baffle to the inlet of the air bag 35. When the gas generator is activated the gas flows along this flow path. The flow path is such that at each point on the flow path the cross-sectional area of the flow path is at least equal to the cross-section of the outlet 26 of the combustion zone 25. Indeed, in the described embodiment, the cross-section of the flow path is non-decreasing from the outlet of the combustion zone to the inlet of the air bag.

Whilst the invention has been described with reference to one embodiment it is to be appreciated that many modifications may be effected without departing from the inventive concept defined by the following Claims.

Claims (12)

CLAIMS:

1. An air bag unit comprising an air bag having an inlet and a gas generator having a gas outlet connected to said inlet by a flow path, the gas generator comprising a first vessel containing a first gas and a second vessel containing a second gas, one of the gases containing oxygen and the other of the gases containing a gas adapted to combust with oxygen, the gas generator comprising means to direct the two gases to a combustion zone where the gases combust when the gas generator is activated, the combustion zone having an outlet which comprises the gas outlet of the gas generator, the combustion zone having a non-decreasing cross-sectional area from the interior of the combustion chamber to the outlet, said flow path having a cross-sectional area which is, at each point on the flow path, at least equal to the cross-section of the outlet of the combustion zone.

2. A unit according to Claim 1 wherein the combustion chamber is of increasing cross-sectional area.

3. A unit according to Claim 1 or Claim 2 wherein the combustion chamber is of annular form, having an annular outlet at the outer periphery of the combustion chamber.

4. A unit according to any one of the preceding Claims wherein one vessel is provided with at least one outlet port, the or each outlet port comprising an aperture sealed by sealing means, there being a piston located adjacent and in supporting relationship with the sealing means adapted to support the sealing means, means being provided to move the piston, when the gas generator is to be activated, to a position in which the piston no longer supports the sealing means, the pressure within the vessel breaking the sealing means or otherwise opening the aperture sealed by the sealing means, thus establishing a flow path to the combustion chamber for gas in that vessel.

5. A unit according to Claim 4 wherein the part of the vessel that defines the sealed aperture or apertures is in the form of a re-entrant well, the piston being mounted for sliding movement on a tubular member extending into the well, there being a flow path between the interior of the tubular member and the end face of the piston, the piston being a substantial sliding sealing fit within the well, there being a gas generating squib provided to supply gas to the tubular member.

6. A unit according to Claim 5 wherein the squib is mounted within an end portion of the tubular member.

7. A unit according to Claim 5 or Claim 6 wherein the second vessel is mounted in position to surround part of the tubular member that projects from the re-entrant well.

8. A unit according to Claim 7 wherein the piston is provided with a peripheral skirt having a plurality of transverse bores therethrough, the piston being adapted to deflect an end wall of the second vessel, thus opening a fluid flow path between the deflected end wall of the second vessel and part of the tubular member on which the second vessel is mounted, that flow path continuing through the transverse bores provided in the skirt of the piston to the combustion chamber.

9. A unit according to any one of the preceding Claims wherein the first vessel contains a mixture of inert gas and oxygen at a pressure of approximately 200 bar, and the second vessel contains hydrogen at a pressure of approximately 30 bar.

10. A unit according to Claim 9 wherein the inert gas is helium.

11. An air bag unit substantially as herein described with reference to and as shown in the accompanying drawings.

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