Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-08-04
2002-07-02
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Attachment
C280S741000
Reexamination Certificate
active
06412814
ABSTRACT:
TECHNICAL FIELD
The invention relates to a gas generator for a safety system, in particular for a vehicle occupant restraint system.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,487,561 discloses a fluid generator which for cooling the generated hot gas uses a fluid which is stored in a chamber surrounding the combustion chamber in a ring shape. If the ignition circuit of the gas generator is now closed, an air chamber is exposed to increased pressure. This leads to a separating member, mounted movably in it, which separates the fluid propellant from the air in the chamber, to be displaced. Through the increased pressure, openings provided in the separating element, which are otherwise tight, become free and the propellant can react exothermically in the air chamber. The generated hot gas can then flow through the openings contained in this chamber into a cooling chamber and can be cooled down by fluid evaporation.
The cooling of the hot gas is therefore necessary because the safety system which is to be filled, in particular the gas bag, can come into contact with vehicle occupants. In order to protect them from burning, the temperature must be cooled down to a compatible extent.
U.S. Pat. No. 5,060,973 discloses a gas generator which has a storage chamber in which liquid propellant is stored and has a reaction chamber in which hot gas is generated and fills the gas bag through openings which are provided. This generator, of course, has no cooling possibilities of any kind.
In the gas generators known hitherto, the fluid injection takes place in an uncontrolled and non-controllable manner, because always the entire fluid is injected.
In the known systems, it is in addition disadvantageous and dangerous if for instance too much fluid is admixed to the hot gas. Through the specific viscosity, the surface tension and the higher inertia of the fluid compared with the gaseous elements of the gas generator, the fluid droplets can not be accelerated as quickly as the gas. In the worst case, this can lead to a blocking, i.e. a clogging, of the openings of the system.
An optimum filling of the gas bag is only possible if a perfectly tempered gas mixture flows into the gas bag in a minimum time span in the millisecond range.
BRIEF SUMMARY OF THE INVENTION
To avoid these disadvantages, the present invention provides a gas generator comprising a combustion chamber filled with propellant, in which a hot gas is generated after igniting and burning of the propellant, a fluid chamber containing a fluid, a mixing chamber in which fluid and hot gas are mixed in a mixture ratio, and at least one control device which controls the mixture ratio of fluid and hot gas in the mixing chamber.
The control device is responsible for the sequence and the development of the injection process. It can be formed by one or more control valves, which is/are in engagement via a gas conduit pipe with the hot gas and the fluid contained in the fluid chamber.
Further, the invention provides for a rapid control of the injected quantity of fluid, which is achieved by at least one control valve, through which the fluid flows and which controls the quantity of fluid flowing into the mixing chamber. The gas generator according to the invention controls, in this embodiment, the quantity of fluid supplied to the hot gas and hence also the mixing ratio of hot gas to injected fluid. The control device is able to provide different mixture ratios. This control takes place directly, i.e. the injected quantity of fluid is not controlled for instance indirectly via the supply of a compressed gas which in turn displaces a separation element, but rather the valve acts directly on the fluid. This has numerous advantages:
The valve is exposed to a cold stream of fluid and not for instance to a hot gas stream. As in the hot gas stream impurities are also entrained, the danger exists of blocking of the valve. However, this can no longer be the case when the fluid flows through the valve. Also a damaging of the valve by the hot gas stream or the entrained impurities is ruled out. Finally, in a valve which control s the hot gas, under pressure, to actuate a displaceable separation element, the valve must be designed both as a ventilation- and also as an evacuation valve. For in order to interrupt the injection process of the liquid propellant, the pressure behind the separation element must be decreased suddenly to the level of the pressure in the mixing chamber. A ventilation- and evacuation valve, however, requires a large space, because it has to have a large cross-sectional area in order to achieve short switching times.
Preferably, the control valve according to the invention is arranged at an outlet of the fluid chamber.
In a further embodiment of the invention, an ejection piston is arranged in the fluid chamber, which piston separates fluid contained in the chamber from the gas which is likewise contained, and is controlled by the control device.
Advantageously, the control device comprises an external control possibility, i.e. one which operates independently of current combustion conditions, such as the generated pressure of the hot gas. This is achieved according to the invention by a lifting magnet which can be controlled in a suitable manner, so that—according to requirements—more or less fluid is injected.
Alternatively, other control elements are also possible, such as a piezo crystal or a rotary drive with threaded spindle.
If the controlling of the injected quantity is to take place exclusively on the basis of the pyrotechnic pressure conditions, then the control device in the form of a valve is triggered as a function of the gas pressure before the valve needle. The gas pressure occurring on the side of the ejection piston adjacent to the valve, and hence the quantity of injected fluid, is proportional to the opening state of the valve. This appears to be useful if for instance the quantity of fuel in the fuel chamber and hence also the quantity of the generated hot gas varies, so that with a reduced quantity of hot gas also less fluid needs to be injected and vice versa.
In the preferred embodiment of the invention, the control device in fact has a combination of the possibilities illustrated in the last two paragraphs, so that the control takes place both on the basis of the generated pressure conditions and also externally.
A preferred embodiment of the invention consists in that the control device regulates the quantity of fluid flowing into the mixing chamber. In so doing, the control device comprises in addition one or more pressure sensors, which detect the pressure of the generated hot gas and pass it on to a preferably microelectronic control- or even regulating unit, which in turn then regulates the stroke of the ejection piston.
In a preferred embodiment, a fluid guiding pipe is arranged downstream of the fluid chamber, in the interior of which pipe the fluid is guided from the fluid chamber to the mixing chamber. The control valve preferably is arranged between the fluid chamber and the fluid guiding pipe, however, it can also be arranged at the end of the fluid guiding pipe.
A simple construction of the valve is achieved in that the fluid pipe has through-flow openings which can be opened to a greater or lesser extent by displacement of a slider which is part of the control valve. The slider is arranged here on the fluid guiding pipe.
In order that the coil which must actuate the slider is as close as possible to the slider, the latter has a tubular part arranged on the fluid pipe and has a, with respect to the pipe, radially outer tubular part. This latter tubular part adjoins the coil. Ribs connect the tubular parts and permit an inflow of the fluid into the cavity between the two tubular parts.
The most varied of restraint systems exist for vehicle occupants. They differ not least according to their installation site in the vehicle, in the type of pyrotechnic propellant which is used and in the filling concept which is applied. Depending on these parameters, with an optimally designed system also the mi
Gabler Michael
Huber Johann
Lindner Markus
Ragner Herbert
Winterhalder Marc
Culbreth Eric
Dunn David R.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Airbag Systems GmbH & Co. KG
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