CA 02204787 1997-0~-07 Li~uid-gas generator The invention relates to a liquid-gas generator according to the preamble of claim 1.
With passive safety devices for motor vehicles, in which inflatable impact protection cushions protect drivers or front seat passengers from injuries caused by impact against the steering wheel or dashboard (also called Air-Bag), either gas generators having a solid propellent charge, or gas generators having condensed gas which is under pressure (hybrid generator, compressed-air generator), or even generators having liquid-gas mixtures which participate in a combustion in a partially active way, are used for the generation of gas. The advantages of gas mixtures in comparison with solid propellent charges when used in a generator are sufficiently known. One problem in the case of gas generators, or even liquid-gas generators, is that the gases which are under pressure must be enclosed in a container which in the case of use, i.e. operational triggering of the generator, must be opened in a defined manner.
A liquid-gas generator for an inflatable impact protection cushion for protecting a motor vehicle passenger from injuries is known from DE 42 41 221 A1.
The liquid-gas generator has a housing in which there is accommodated a reaction container with liquid-gas.
In order to trigger combustion of the liquid-gas, a piercing element having a transfer duct is driven into the reaction container. The kinetic energy for the piercing element is produced pyrotechnically by initiating an igniter element. The ignition vapours of the igniter element reach the inside of the reaction container by way of the transfer duct, and there initiate the combustion of the liquid gas. The combustion gases which are produced in this connection CA 02204787 1997-0~-07 emerge from the reaction container by way of the transfer duct and reach a chamber in which the piercing element is arranged. The chamber is closed from a discharge space (through-passage) by a rupture membrane. This rupture membrane breaks when a minimum pressure of the combustion gases is reached and consequently frees the way for removal of the combustion gases from the housing by way of the discharge space (through-passage).
A disadvantage of this is that the piercing element, or the firing piece, has to rest directly against the reaction container, because otherwise a pressure can build up behind the firing piece that prevents the reaction container from being pierced.
Apart from this there is the danger that the firing piece will be asymmetrically loaded, something which in turn can lead to uncertainties with the piercing. A
substantial disadvantage is, furthermore, the rupture membrane which is required and by means of which the chamber is constructed as a pressure space. Firstly, these rupture membranes are extremely expensive and secondly, when only one rupture membrane is used, a reaction is produced by the gas which emerges, which reaction imparts an undesired rotational moment to the gas generator.
The underlying object of the invention is to improve a liquid-gas generator according to the preamble of claim 1 in such a way that the opening or piercing of the reaction container is simplified, and such that for the whole duration of the operation, the generation of gas takes place in a controlled and reproducible manner.
In order to achieve this ob;ect, in accordance with the invention, a liquid-gas generator is proposed, the housing of which contains a closed reaction container for accommodating liquid-gas. Formed in the - CA 02204787 1997-0~-07 housing is a chamber, which abuts the reaction container when the latter is inserted. Displaceably arranged in the chamber there is a piercing element, the whole length of which is driven through the wall of the reaction container when an igniter element is ignited and plunges completely into the reaction container. As a result of the piercing or puncturing of the wall of the reaction container by the piercing element, and the further penetration of the piercing element into the reaction container, which was previously closed, there is consequently a connection with the diameter of the piercing element.
A substantial advantage lies in the fact that there is no separate pressure space having a rupture dis~. As a result of this, a decisive price advantage is given. Because there is no rupture disc, a symmetrical discharge is to be achieved simply by a comparatively lar~e number of discharge passages over the diameter. As a result of this a reaction or an undesired rotational moment is prevented. A further advantage consists in the simple structure of the gas generator, which is to be produced almost solely from rotationally-symmetrical components.
The piercing element is advantageously a solid body.
In a preferred embodiment in accordance with the invention, for better piercing/puncturing of the wall of the reaction container, the piercing element has the shape of a projectile, i.e. a cylinder with a cone, sphere, cylinder, etc mounted thereon.
In an advantageous embodiment, the igniter element contains a primer capsule.
In order to trigger the liquid-gas generator, the igniter element or the primer capsule is ignited. The combustion gases which are produced when the igniter element is ignited drive the piercing element through CA 02204787 1997-0~-07 the wall of the reaction container. In this case, igniter element and piercing element are connected to each other in such a way that a clean puncturing of the separating wall is guaranteed in each case. Because the hot gases which follow penetrate into the reaction container, and the liquid gas mixture flows out into the chamber, ignition and reaction of the liquid-gas mixture result. The combustion gases which are produced are led off by transfer ducts which lead off from the chamber. As a result of shape, position and diameter of the transfer ducts, the generation of gas can be controlled and can take place in a reproducible manner. As a result of this, the use of expensive rupture discs in this region can be eliminated. The combustion gases which enter the transfer ducts emerge from the gas generator by way of discharge passages in the housing, and then inflate the folded impact protection cushion.
As already mentioned, the piercing element advantageously has the shape of a projectile in order to guarantee a certain and defined piercing of the separating wall. The piercing element is advantageously connected to the igniter element or a sleeve by way of a tear-off edge, so that only after a defined pressure has been produced, caused by the combustion gases of the igniter element, can the piercing element begin to move with high energy.
Alternatively, a radial extension can be arranged on the piercing element and/or a radial narrowing can be arranged in the guide sleeve.
In order to achieve the energy which is required for piercing the wall, there is advantageously arranged between the piercing element and the igniter element a chamber (utilisation of the combustion gases). The chamber is advantageously filled with a charge. The charge is advantageously a pyrotechnic propellent CA 02204787 1997-0~-07 charge powder or ignition composition such as e.g.
nitrocellulose, a boron-potassium nitrate mixture or a black-powder mixture. In accordance with the invention, the igniter element is advantageously provided with a cylindrical guide sleeve for guiding the piercing element.
The piercing element advantageously consists of a temperature stable combustible moulded part, which, after penetrating into the reaction container, is combusted by the high temperature which occurs during the reaction of the gas. A further advantage is the fact that, in the event of the piercing element flowing back through the opening, the piercing element can no longer block a transfer duct during combustion. The piercing element, the tear-off edge and the sleeve are preferably one moulded part.
The wall of the reaction container that is to be broken down by the piercing element is advantageously a rupture disc, which is preferably integrated in the lid of a sealing cap of the reaction container.
Further features arise from the figures, which are described in the following.
~Figure 1 shows in section a liquid-gas generator in accordance with the invention, Figure 2 shows in part section a first embodiment of an igniter element and Figure 3 shows in section a second embodiment of an igniter element.
Figure 1 shows a liquid-gas generator 1 in accordance with the invention, which liquid-gas generator ~ubstantially comprises a head portion ~, a base portion or adapter 9 and a cylindrical discharge pipe 10. Arranged in the discharge pipe 10 are discharge passages 11. Apart from this there is arranged in the discharge pipe 10, or in the liquid-gas generator 1, a reaction container 7 as a self-pressure-` CA 02204787 1997-0~-07 , resistant bottle. Liquid gas, or a liquid-gas mixture, is located in this reaction container 7.
The reaction container 7 is used as a storage container as well as a combustion chamber for the liquid-gas mixture. The end face of the reaction container 7 is closed by way of a rupture disc 5. The rupture disc 5 is in this case integrated in the lid of a sealing cap 18. This sealing cap 18 is screwed into the head portion 2 by way of a thread 20, in such a way that a chamber 19 abuts the rupture disc 5. From the chamber 19, transfer ducts 6 lead out into the spacing between reaction container 7 and discharge pipe 10.
Arranged in the head portion 2 there is furthermore an igniter element holder 3 having an igniter element 4.
The front point of the igniter element 4 has a piercing element 16 having the shape of a projectile and pro;ects with said piercing element into the chamber 19. The igniter element 4 lies on the longitudinal axis 21 of the reaction container 7.
The reaction container 7 is advantageously made from tempered steel. The housing is likewise advantageously made from steel or aluminium.
Figure 3 shows a variant of the igniter element 4.
The igniter element 4 is inserted into the igniter element holder 3. The igniter element 4 comprises a primer capsule 12 and a chamber between piercing element 16 and primer capsule 12, which chamber is filled with a charge 13. The piercing element 16 is securely connected to the igniter element 4 by moulding over a sleeve 14 having a tear-off edge 15. In the event of ignition, the igniter element 4 is ignited, the gases and heated particles which are produced ignite the charge 13. Because the piercing element 16, which is securely connected to the igniter element holder 3 by way of the sleeve 14 and the tear-off edge 15, cannot start to move, a build-up of pressure CA 02204787 1997-0~-07 determined by the strength of the tear-off edge 15 results. After a certain defined pressure has been reached, then a tearing off between the piercing element 16 and the sleeve 14 takes place very quickly at the tear-off edge 15. As a result of the guide sleeve 17 of the igniter element holder 3, a directed acceleration of the piercing element 16 occurs. The piercing element is accelerated in a defined manner in the guide sleeve 17 by the combustion-gas pressure (principle of a bullet in a short barrel).
After the piercing element 16 has been separated from the igniter element holder 3 or igniter element 4, the piercing element 16 traverses the chamber 19 of the head portion 2 and pierces the rupture disc 5, which separates the liquid-gas mixture in the combustion chamber 8 from the head portion 2 or chamber 19 (see Figure 1). The liquid-gas mixture is ignited in the combustion chamber 8 by the hot gases and hot particles of the igniter element 4 which follow the piercing element 16. A volume expansion takes place into the chamber 19 of the head portion 2 via the opening in the rupture disc 5, and consequently the inflation of the gas sack begins via the transfer ducts 6 and the discharge passages 11. Gas development and pressure increase in the chamber 19 of the head portion 2 can be controlled in a defined manner by position, diameter and by the number of discharge ducts 6. The piercing element 16 can consist of a temperature stable combustible moulded part (plastics material or metal), which has the shape of a projectile. As a result of the high temperature which results during the reaction of the li~uid-gas mixture, the piercing element 16 combusts after it has penetrated into the combustion chamber 8.
Figure 2 shows an embodiment of the piercing element 16 and the charge 13 that is somewhat different CA 02204787 1997-0~-07 to Figure 3. The piercing element 16 is here not connected to the sleeve 14 or the igniter element 4 by way of a tear-off edge 15. Instead of this, a radial extension 31 is arranged on the piercing element.
Alternatively, a radial narrowing 30 can also be provided in the guide sleeve. Both measures effect, as does the tear-off edge 15 in Figure 3, a directed acceleration of the piercing element 16 only after a certain pressure has been reached.