Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-12-15
2001-03-06
Rice, Kenneth R. (Department: 3611)
Land vehicles
Wheeled
Attachment
C280S741000
Reexamination Certificate
active
06196583
ABSTRACT:
The invention relates to an inflator for a safety device, in particular for a vehicle occupant restraint system, comprising a housing, a combustion chamber formed in the housing and including a solid propellant for generating hot gas, and a coolant introduced into a predetermined flow path of the hot gas.
Conventional pyrotechnical inflators contain a propellant charge introduced into a combustion chamber, which, after an electric pulse has been triggered by a sensor due to a crash, is ignited by means of an ignition unit integrated in the inflator. The propellant charge is usually a solid propellant on the basis of sodium azide (NaN
3
) and an oxidant such as for example KNO
3
. Due to the toxicity of the sodium azide, sodium azide-free propellants are finding more recent application. However, to maintain the permissible maximum concentrations of the resulting undesirable side products of combustion, these sodium azide-free propellants often feature a higher combustion temperature than that of conventional propellants on a sodium azide basis. This is why attempts are made, in employing sodium azide-free propellants, to cool the hot gas generated on ignition of the inflator by a pyrotechnical igniter using filter units or other means prior to the hot gas entering the gas bag.
U.S. Pat. No. 5,487,561 describes a liquid gas generator in which a liquid coolant of calcium chloride dissolved in water is held in a chamber annularly surrounding the combustion chamber containing the liquid gas. Following ignition of the inflator the released hot gas flows through the liquid coolant chamber and vaporizes the liquid coolant at least in part, as a result of which thermal energy is drawn from the flow of hot gas.
Published German patent application DE-OS 22 29 039 describes an inflator having a combustion chamber and downstream thereof a cooling chamber containing a vaporable coolant such as e.g. a halocarbon. The hot gases generated in the combustion chamber first pass through a filter unit or reaction chamber and then through a nozzle plate separating the reaction chamber from the coolant chamber. The hot gases entering the coolant chamber through the nozzle cause the coolant to be swirled and evaporated, and thus the hot gas flow to be cooled.
Finally, the not pre-published German patent application DE 196 02 695 discloses an inflator in which a fluid-tight liquid coolant container is arranged in a flow space outside of the combustion chamber. The hot gas emerging from the combustion chamber burns through the casing of the container and strikes an expanded silicone rubber saturated with liquid coolant. Due to the evaporation of the liquid coolant the hot gas is further cooled.
All of the documents cited above describe differing arrangements and means of storing the coolant. However, adequate cooling of the hot gases generated by the inflator is only possible when a precisely defined distribution of the droplets of the coolant is assured. Where porous or capillary substrate materials are employed in the systems mentioned above, no such homogenous distribution of the coolant for generating surface areas having a high specific volume can be achieved since due to the high hot gas velocities involved, the frictional resistance occurring in the capillaries and the kinematic viscosity of the coolant employed is too large to set the coolant free from the substrate material in the short time available. Instead, the coolant is pushed out of the capillaries by the hot gas without atomization of the liquid being attained.
Providing greater liquid volumes for cooling the hot gases directly upstream of the exit ports of the inflator may easily result in the exit ports becoming totally clogged, thus fractionating the inflator since the inertia of the coolant employed as well as its viscosity and surface tension do not permit accelerating the droplets of coolant to the hot gas velocity. In this case an ever-increasing pressure materializes in the combustion chamber, and the burning rate of the propellant is further increased due to the high pressure, resulting in the overall system quickly assuming an unstable burning state which may lead to total disintegration of the inflator. A further drawback of the systems known from the cited prior art is the use of a storage medium for liquid coolants which is large in volume as compared to the system as a whole, this resulting in an undesirable mass increase of the inflator.
To avoid these drawbacks the present invention provides an inflator of the aforementioned kind which is characterized in that the flow path of the hot gas passes through a nozzle contour comprising a pitot zone in which the hot gas emerging from the combustion chamber has a high static pressure, and comprising a nozzle neck in which the hot gas builds up a high dynamic pressure, the coolant being arranged in a sleeve-shaped reservoir extending from the region of the pitot zone at least in part into the nozzle neck.
In this arrangement the reservoir for the coolant is preferably provided in the region of the pitot zone of the nozzle contour with radial pressure-relief ports. Furthermore, the sleeve-shaped reservoir may be provided in the region of the nozzle neck with one or more openings. These openings are preferably located on the end face of the reservoir and are set back relative to the downstream end of the nozzle neck, as a result of which in the upper end of the nozzle neck a mixing zone for the hot gas and the coolant is formed. Preferably, the coolant is enclosed in the reservoir in a burstable casing, which may be made, for example, of aluminum or a plastics material.
In a preferred embodiment the housing of the inflator in accordance with the invention is configured tubular and consists essentially of an upper housing part and a lower housing part. In this arrangement, the nozzle contour is arranged in the upper housing part and coaxially to the combustion chamber formed in the lower housing part, the wall of the upper housing part preferably locating the nozzle contour centered. In this embodiment the combustion chamber is preferably separated from the nozzle contour by a perforated plate having bore holes for the exit of the hot gas towards the nozzle. The sleeve-shaped reservoir for the coolant may be centrally secured to the perforated plate and be arranged coaxially to the nozzle contour.
In a further embodiment of the invention the inflator housing consists of a pot-shaped lower housing part and a cover-like upper housing part. In the middle of the upper housing part a sleeve including an igniter is arranged which in the region of the igniter is filled with a pyrotechnical booster charge. The reservoir for the coolant is located on the side of the sleeve opposite the igniter and is separated from the pyrotechnical booster charge by a pressure plate. In this embodiment the combustion chamber preferably annularly surrounds the sleeve containing the coolant and the pyrotechnical booster charge. The nozzle contour is located in the middle of a nozzle plate press-mounted in the lower housing part, the sleeve protruding at least in part into the nozzle contour.
In all of the embodiments of the invention described the solid propellant may be present in the form of pills, pellets, rings or compacts or may have any other form known in the art.
The coolant employed is preferably a fluid having a freezing point of below −35° C. to ensure proper functioning of the inflator even under winter conditions.
The present invention comprises a thermally improved inflator whereby the hot gases resulting from ignition of the igniter and combustion of the propellant are cooled by a coolant contained in the inflator. In so doing, the coolant is vaporized, which in turn contributes towards a desired increase in volume of the flow of hot gas. Due to the extremely rapid combustion process the coolant employed also needs to be vaporized in this short time to achieve a further increase in volume and thus an enhanced performance, at the same time having cooler exhaust gases. To achieve a high h
Fink Martin
Hinterberger Christof
Laucht Horst
Leifheit Markus
Lindner Markus
Rice Kenneth R.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Airbag Systems GmbH & Co. KG
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