Gas generator

A gas generator for generating gas under pressure. The gas generator comprises a device for providing a first gas including a pressure vessel containing the first gas, the first gas being an oxidizing gas; a device for providing a second gas adapted to be oxidized by the first gas and including a pyrotechnic charge for generating the second gas when ignited. An oxidation zone of the gas generator includes an outlet, the first gas and the second gas being adapted to undergo an oxidation reaction in the oxidation zone for generating the gas under pressure. The first gas and the second gas are directed to the oxidation zone such that the oxidation zone contains a mixture of the first gas and the second gas for the oxidation reaction thereof, the second gas being of a sufficiently elevated temperature to initiate the oxidation reaction in the oxidation zone. A back-up catalytic device ensures initiation of the oxidation reaction of the mixture.

FIELD OF THE INVENTION 
The present invention relates to a gas generator and more particularly 
relates to a gas generator adapted for use in inflating an air-bag in a 
motor vehicle. 
BACKGROUND OF THE INVENTION 
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 "self-combusting". 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. Also the gas generated following 
ignition of a pyrotechnic material may contain poisonous gasses, such as 
carbonmonoxide, or potentially explosive gasses, such as hydrogen. 
The object of the present invention is to provide an improved gas generator 
which is capable of generating gas very swiftly, but which is safe. 
SUMMARY OF THE INVENTION 
According to one aspect of this invention, there is provided a gas 
generator comprising means for providing a first, oxidizing, gas and a 
second gas adapted to be oxidized by said first gas, the gas generator 
comprising means, when the gas generator is activated, to direct the first 
gas and the second gas to an oxidation zone where the gases react, the 
oxidation zone having an outlet, catalytic means being provided associated 
with the oxidation zone to initiate the reaction between the mixed gases 
when the mixed gases are introduced to the oxidation zone. 
The oxidizing gas may be oxygen, or a gas containing oxygen such as nitrous 
oxide. The second gas may comprise hydrogen, or a hydrocarbon such as 
methane or ethane, or may comprise carbonmonoxide. Typically, therefore, 
the oxidation reaction is a combustion reaction. 
In one embodiment the first gas and the second gas are initially contained 
within a single pressure vessel. 
Conveniently, additionally an inert gas, such as argon and/or helium is 
present within the pressure vessel. 
In an alternative embodiment, the first gas and the second gas are 
initially contained in separate respective pressure vessels. 
Preferably, additionally an inert gas, such as argon and/or helium, is 
present within each of the pressure vessels. 
Conveniently, electrically controlled valve means are located between the 
pressure vessel or vessels and the oxidation zone, the valve means being 
adapted to be opened in response to an accident. 
Alternatively, the gas generator comprises a pyrotechnic charge which when 
ignited generates said second gas, and a pressure vessel containing said 
first gas. 
In such an embodiment, the pressure vessel may also contain an inert gas, 
such as argon and/or helium. 
Conveniently, an electrically activated squib is provided to ignite the 
pyrotechnic charge, and or electrically actuated valve is provided between 
the pressure vessel and the oxidation zone, both the squib and the valve 
being adapted to be activated by a signal from a sensor. 
According to another aspect of this invention, there is provided a 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, when the gas generator is activated, to 
direct the two gases to a combustion zone where the gases combust, the 
combustion zone having an outlet, catalytic means being provided within 
the combustion zone to ignite the mixed gases when the mixed gases are 
introduced to the combustion zone. 
It is to be understood, therefore, that in this embodiment no separately 
acting means is provided to ignite the gas mixture--instead the gas 
mixture is ignited by the catalyst. This facilitates the use of two 
separate gases which can be mixed and combusted within the combustion 
chamber. Since two separate gases are utilised, stored in separate 
vessels, there is not the risk of unintentional combustion that is 
associated with the use of a pyrotechnic material. 
Preferably, the catalytic means comprise a catalytic inert metal, such as a 
metal selected from the group comprising platinum, osmium, iridium, 
palladium, rhodium and ruthenium, the preferred metal being platinum. The 
catalyst may be supported on a porous substrate such as alumina, asbestos 
or silica. 
Advantageously, additionally a pyrotechnic or electric igniter is 
associated with the combustion zone to ensure ignition of the mixed gases. 
Preferably, one vessel is provided with at least one 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. Moreover, means are 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. 
Advantageously, 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 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 providing a substantial sliding sealing fit within 
the well. Moreover, a gas generating squib is provided to supply gas to 
the tubular member. 
Conveniently, the squib is mounted within an end portion of the tubular 
member. 
Advantageously the second vessel is mounted in position to surround part of 
the tubular member projecting 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. The flow path 
continues through the transverse bores provided in the skirt of the piston 
to the combustion zone. 
Conveniently, 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. 
Advantageously, the inert gas is helium.

DETAILED DESCRIPTION OF THE INVENTION 
Referring initially to FIG. 1, a gas generator in accordance with the 
invention comprises an arrangement 1 for delivering an oxidizable gas and 
an oxidizing gas to a combustion chamber 2. The combustion chamber 3 is 
associated with a catalytic device which facilitates or enables the 
oxidation of the oxidizable gas. Such oxidation is most frequently 
associated with the generation of heat. The oxidized gas passes from the 
combustion chamber to a safety device 4 provided in a motor vehicle such 
as an air-bag or a seat-belt pre-tensioner. The entire arrangement is 
activated by a crash sensor 5 which triggers operation of the arrangement 
for delivering the oxidizable gas and the oxidising gas. 
As will become clear from the following description, many different 
detailed arrangements may be provided for delivering the oxidisable gas 
and the oxidising gas, but once the gases have passed through the 
combustion chamber 2, and combustion has been initiated by the catalytic 
device, the gas that is passed on to the safety device 4 does not contain 
any significant quantities of oxidizable gas such as carbonmonoxide or 
hydrogen. 
Referring now to FIG. 2 of the accompanying drawings which illustrates one 
embodiment of the invention, the illustrated arrangement comprises a first 
pressure vessel 10 which contains fuel, such as hydrogen and inert gas. 
The inert gas may be argon, helium or a mixture of these gases. The 
arrangement includes a second pressure vessel 11 which contains oxygen 
admixed with an inert gas. The inert gas in the second pressure vessel 11 
may also comprise argon, helium or a mixture of these gases. 
The first pressure vessel 10 has an outlet 12 and the second pressure 
vessel 11 has an outlet 13, the outlets 12 and 13 being connected, through 
an electrically activated valve arrangement 14 to an inlet 15 of a 
combustion chamber 16. The electrically operated valve 14 has electric 
leads connected to a crash sensor, such as the crash sensor 5. 
Contained within the combustion chamber 16 is a catalytic igniter 17. The 
catalytic igniter comprises a catalytic inert metal, such as a metal 
selected from a group comprising platinum, osmium, iridium, palladium, 
rhodium and ruthenium supported on a porous substrate such as alumina, 
asbestos or silica. The preferred metal is platinum. The catalyst may be 
in the form of a thin film provided on the porous substrate or may be 
present in the form of a block. 
The combustion chamber 16 is provided with an outlet 18 which extends to a 
safety device in the form, in this example, of an air-bag 19. 
Optionally, the inlet 15 to the combustion chamber 16 is provided with an 
electric or pyrotechnic igniter 20. In operation of the arrangement 
illustrated in FIG. 2, in the event that an accident should arise, the 
electrically actuated valve 14 is opened permitting the fuel mixed with 
inert gas from the first pressure vessel 10 and the oxygen mixed with 
inert gas from the pressure vessel 11 to flow through the inlet 15 into 
the combustion chamber 16. Oxidation of the fuel is then initiated by the 
operation of the catalytic igniter 17. If the optional pyrotechnic or 
electric igniter 20 is present, it will be activated in response to a 
signal from the crash sensor which opens the electrically activated valve 
14. In such a case the catalytic igniter is primarily provided as a 
precautionary step, as a back-up which ensures ignition in cold weather or 
other adverse conditions. 
It will be appreciated, however, that the fuel will be oxidized within the 
combustion chamber 16. This will increase the temperature of the gas and 
the chemical reaction of combustion may be such that at the end of the 
reaction, more molecules are present than were present at the commencement 
of the reaction, thus further increasing gas pressure. Gas at an elevated 
temperature and at a high pressure will flow through the outlet 18, thus 
rapidly inflating the air-bag 19. The gas entering the air-bag 19 will not 
contain significant quantities of carbon monoxide or hydrogen. 
In the arrangement of FIG. 2, it is to be observed that the fuel and the 
oxygen are initially maintained in separate pressure vessels 10 and 11. 
There is thus virtually no risk of the fuel being ignited inadvertently. 
FIG. 3 illustrates a simplified embodiment of the invention, with many 
parts common with the embodiment of FIG. 2. The same reference numerals 
will be used for the same parts. 
It is to be noted, however, that in the embodiment of FIG. 3, there is only 
a single pressure vessel 10 which contains fuel such as methane or ethane, 
oxygen (or an oxidizing gas such as nitrous oxide) and inert gas, the 
inert gas being argon, helium or a mixture of these gases. The single 
pressure vessel 10 has a single outlet 12 connected by means of the 
electrically activated valve 14 to the inlet 15 of the combustion chamber 
16, which again has the catalytic igniter 17. The combustion chamber 16 
has an outlet 18 illustrated as being connected to an air-bag 19. Again an 
optional electric or pyrotechnic igniter 20 is provided associated with 
the inlet 15 to the combustion chamber 16. 
In operation of the arrangement illustrated in FIG. 3, the electrically 
operated valve 14 will be opened permitting the pressurised gas within the 
pressure vessel 10 to flow into the combustion chamber 16. Combustion of 
the fuel will be initiated by the catalytic igniter 17 and, if the 
electric or pyrotechnic igniter 20 is provided, combustion will also be 
initiated by that igniter. 
As in the arrangement illustrated in FIG. 2, gas under high pressure at an 
elevated temperature will flow through the outlet 18 to inflate the 
air-bag 19. The gas will not contain any significant quantities of carbon 
monoxide or hydrogen. 
Referring now to FIG. 4 of the drawings, a gas generator arrangement for 
inflating an air-bag comprises a housing 21 containing a pyrotechnic 
charge 22. The pyrotechnic charge may be of any appropriate pyrotechnic 
material which, when ignited, rapidly produces a large quantity of gas. 
The preferred pyrotechnic charge comprises a mixture of Nitrocellulose and 
Nitroglycerine which, when ignited, produces a mixture of gases which 
comprise 23% carbon dioxide, 15% nitrogen, 42% carbon monoxide and 20% 
hydrogen. 
Contained within the housing 21 is an electrically triggered pyrotechnic 
igniter squib 23 which is connected to electric leads 24 which in turn are 
connected to a crash sensor (not shown). The arrangement is such that when 
a crash is sensed by the crash sensor an electric impulse is transmitted 
through the electric leads 24 to the igniter squib 23 which thus ignites 
the pyrotechnic material 22. 
The housing 1 has an outlet conduit 25 which extends to a combustion 
chamber 26 (which will be described hereinafter), the combustion chamber 
26 having an outlet leading directly to an air-bag 27. Consequently, when 
a crash is sensed by the crash sensor and the pyrotechnic material 22 is 
ignited, gas from the pyrotechnic material inflates the air-bag 27. 
The described gas generating arrangement additionally includes a second 
housing in the form of a pressure vessel 28 which contains a compressed 
gas. At least part of the compressed gas comprises oxygen. It is preferred 
that the compressed gas also contains other inert gas and in one 
particular arrangement the vessel 28 contains 80% argon, 10% helium and 
10% oxygen. It has been found that argon has good heat absorbing 
properties, whereas helium facilitates the detection of leaks. 
An outlet port 29 from the pressure vessel is connected, through an 
electrically actuated valve 30 to the combustion chamber 26. The 
electrically actuated valve 30 is connected to the electric leads 24 which 
receive the signal from the crash sensor in such a way that when the crash 
sensor senses a crash the electrically controlled valve is opened. 
Contained within the combustion chamber 26 is a catalytic igniter 31. The 
catalytic igniter comprises a catalytic inert metal, such as a metal 
selected from the group comprising platinum, osmium, iridium, palladium, 
rhodium and ruthenium supported on a porous substrate such as alumina, 
asbestos or silica. The preferred metal is platinum. The catalyst may be 
in the form of a thin film provided on the porous substrate, or may be 
present in the form of a block. 
It is to be appreciated that in operation of the arrangement illustrated in 
FIG. 4, when the crash sensor senses a crash, the pyrotechnic charge 22 is 
ignited and also the electrically actuated valve is opened. The combustion 
gases from the pyrotechnic charge and the gas present within the pressure 
vessel are thus simultaneously directed towards the combustion chamber 26. 
The gas from the pyrotechnic charge is at an elevated temperature, and 
when mixed with the gas from the pressure vessel, which contains oxygen, 
the oxidisable components of the gas from the pyrotechnic charge are 
oxidized. The oxidation reaction commences immediately due to the high 
temperature of the gas. Thus the hydrogen burns to from water and the 
carbon monoxide is further oxidized to form a carbon dioxide. The 
catalytic igniter is provided as a back-up to ensure that the oxidation 
reactions do occur. 
Consequently, the gas leaving the combustion chamber 26 is fully oxidized 
and does not contain any significant quantities of carbonmonoxide or 
hydrogen. 
The embodiment of FIG. 4 may also be provided with an optional electric or 
pyrotechnic igniter 32. 
Referring now to FIG. 5, an air bag unit incorporates a gas generator which 
comprises a first gas-containing gas bottle 41 of cylindrical form having 
one end closed by a closure plate 42 which is welded 43 or otherwise 
secured to the housing 41 of the gas bottle. The closure plate 42 is of 
circular form, but defines a central inwardly directed, or reentrant well 
44, which is of circular cross-section. The well 44 effectively forms a 
cylindrical side wall 45 which is co-axial with the housing 41 but of a 
lesser radius, and also defines an end wall 46 forming the bottom of the 
well. 
A plurality of apertures 47 are provided in the side wall 45 at equi-spaced 
positions, but only one aperture is shown in FIG. 5. The aperture is 
initially sealed by means of a sealing disc 48 formed of a relatively 
thin, but gas-tight material, such as aluminium foil, which may be 
soldered or welded in position. 
A plurality of passages 49 are defined by projections 50 provided at the 
open end of a tubular flame-guide element 52. The projections 50 are 
provided at the end of a portion 53 of a first diameter. The tubular 
element has an enlarged end 54 remote from the portion 53, that enlarged 
end 54 containing an ignition squib 55. 
A piston 56 is provided, mounted for sliding movement along the lesser 
diameter portion 53 of the tubular element 52. The piston provides a 
sliding substantially sealing fit within the well. The piston 56 has an 
initial position within the well 44. When in this position, a side wall 57 
of the piston is located adjacent the foil element 48 sealing the aperture 
47. The piston thus supports the foil element 48. 
The piston has a rearwardly directed skirt 58 provided with a plurality of 
small diameter transverse bores 59 which form a flow path from a space 60 
which is located on the interior of the skirt 58 of the piston, to the 
outer wall 57 of the piston. 
Mounted on the enlarged diameter portion 54 of the tubular element 52 is a 
second gas-containing housing comprising a cylindrical side wall 61 
carrying a first inwardly directed end wall 62 which is securely connected 
to the end of the enlarged diameter portion 54 of the tubular element 62 
and a second inwardly directed end wall 63 which contacts the exterior of 
the enlarged diameter portion 54 of the tubular element 52 in a sealing 
manner. 
Mounted on the part of the end cap 42 adjacent the housing 41 and also 
mounted on the end wall 63 of the second gas-containing housing are a 
plurality of elements 64 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 41, 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 48 against the side wall 57 of the piston. 
The piston supports the sealing disc 48. The disc 48 thus seals the 
aperture 47. 
The second gas bottle, defined by the side wall 61 and the end walls 62,63 
contains hydrogen at a pressure of 30 bar. Inert gas may, if desired, be 
combined with the hydrogen. 
The space 65 between the end cap 42 and the end wall 63 forms a combustion 
zone. The outlet 66 of the combustion zone is an annular outlet located at 
the periphery of the space 65, in alignment with the cylindrical wall 
gas-containing housing 41 and the cylindrical wall 61 of the second 
gas-containing bottle. It is thus to be appreciated that the combustion 
space 65 is effectively of increasing cross-sectional area in a plane 
transverse to the longitudinal axis of the air bag unit from its interior, 
adjacent the tubular member 52, to its termination or outlet, i.e. the 
annular outlet 66 in alignment with the side wall of the gas bottle 41 and 
the side wall 61. 
In operation of the gas generator as described with reference to FIG. 5, 
initially the squib 55 is ignited in response to a signal from an accident 
sensor. Gas generated from the squib passed down the tubular element 52, 
through the spaces 49 inbetween the projections 50 and the gas thus 
engages the end face of the piston 56. The piston 56 is thus driven to 
move towards the left as shown in FIG. 5, the piston thus reaching the 
position shown in FIG. 6. The movement of the piston has two effects. 
Firstly, the side wall 57 of the piston 56 no longer supports the sealing 
disc 48 present in the aperture 47. The sealing disc 48 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 57 of the 
piston 56. Whilst the sealing disc 48 was able to withstand the applied 
pressure when supported by the side wall 57 of the piston 56, when no 
longer supported the sealing disc ruptures thus permitting the helium and 
oxygen mixture to flow, as indicated by the arrow 67, from the interior of 
the gas bottle, through the aperture 47, past the tubular member 52, past 
the piston 56 and into the combustion chamber 65. 
Secondly, the movement of the piston causes the skirt 58 of the piston to 
engage and deflect inwardly the end wall 63 of the gas bottle containing 
hydrogen. This opens a flow path between the end of the wall 63 and the 
exterior of the enlarged diameter portion 54 of the tubular member 52 for 
the hydrogen gas from within the second gas bottle. The hydrogen gas flows 
within the skirt 58 of the piston 56 and then flows through the radially 
extending bores 59 into the combustion space 65, as indicated by arrow 68. 
The hydrogen is thus mixed in the combustion space with the helium and 
oxygen gas. The resultant mixture is ignited by the catalyst element 64. 
Because the combustion space 65 continually diverges towards its outlet 66 
or, in other words, continually has an increasing cross-section as the gas 
advances towards the outlet 66, 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 69. The end wall 62 of the second gas bottle is connected to a 
side wall of the housing 69. An aperture present in the side wall provides 
communication with the squib 55. 
The outlet 66 of the combustion chamber communicates with an annular space 
71 which surrounds the first gas bottle 41 and the side wall 61 of the 
second gas bottle. 
A baffle 72 having apertures 73 bounds part of the annular space 71 and 
separates that space from a chamber 74 which contains a folded air bag 75. 
The chamber 74 is closed by a cover 76 which retains the folded air bag 75 
in position. The cover 76 is connected to the housing 69. 
The apertures 73 in the baffle 72 effectively form an inlet for the air 
bag. 
It is to be noted that a flow path exists through the annular space 71 from 
the outlet 66 of the combustion space 65, to the baffle 72 and thus 
through the apertures 73 in the baffle to the inlet of the air bag 75. 
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 in a plane transverse to the 
longitudinal axis of the air bag unit is at least equal to the 
cross-section of the outlet 66 of the combustion zone 65. 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 particular 
embodiments, it is to be appreciated that many modifications may be 
effected without departing from the inventive concept defined by the 
following claims.