Patent Application
20070085310
The present invention relates to a gas generator for a vehicle occupant restraint system as well as to an airbag module having such a gas generator. The gas generator includes a gas generator housing defining a distribution chamber and a generator chamber from which gas flows into the distribution chamber after the gas generator has been activated, the distribution chamber having at least one first outflow opening that conveys the gas into an airbag.
The use of airbag modules in which an airbag can be filled with gas by means of a gas generator is a standard feature of modern vehicle occupant restraint systems. In order to be able to produce such airbag modules cost-effectively in large numbers of units, the industry endeavors to use identical components to the greatest extent possible. In addition to the advantage in terms of the production of the module, this also translates into advantages for the assembly of the airbag module, since a uniform installation space as well as a standardized attachment can be provided. Another objective pertaining to the production of airbag modules is the simple adaptation of the modules to customer wishes, to special aspects of a given vehicle series or to different international regulations and requirements made of vehicle occupant restraint systems. It would be particularly advantageous if these adaptations of the airbag module could be made merely through structural changes to one or just a few components of the module assembly such as, for example, to the gas generator.
Consequently, the object of the present invention is to further develop an existing airbag module system in such a way that additional requirements such as the venting of generator gas into the environment can be met especially simply and efficiently.
According to the invention this is achieved in a gas generator for a vehicle occupant restraint system including a gas generator housing, the gas generator housing defining a distribution chamber and a generator chamber from which gas flows into the distribution chamber after the gas generator has been activated, the distribution chamber having at least one first outflow opening that conveys the gas into an airbag, the distribution chamber further having a pyrotechnical device that, when it is triggered, releases at least one second outflow opening in order to discharge gas to the environment.
Venting the gas directly from the gas generator is particularly efficient whenever generator gas—which for various reasons is not to be used for filling the airbag—has to be quickly discharged into the environment. After all, due to the high gas pressures built up in the gas generator, a large mass flow can be released through relatively small outflow openings. Moreover, this prevents unneeded gas from first flowing into the airbag in order to then flow back out via openings in the airbag. This is especially unwanted if the vehicle occupant is not seated in an optimal restraint position and if the deployment speed of the airbag should thus be low. Moreover, by means of the gas generator according to the invention, a possibility for venting generator gas is created in which no additional changes have to be made to the airbag or to a nodule housing. Furthermore, no additional openings, tethers or limiting straps are needed. A pyrotechnical device as the triggering means is particularly advantageous in view of its relatively low cost and short response time. As a rule, the use of more expensive, reversible triggering means does not entail any advantages since the relevant time periods of a few milliseconds are too short to pick up sensor signals several times in succession, to process them and to activate the triggering means accordingly.
The distribution chamber is preferably a one-piece component of the gas generator. As an alternative, it is made up of one or more parts that are permanently attached, especially by means of welding, to the rest of the generator, for example, to the outer wall of the generator chamber.
In one embodiment, the pyrotechnical device is an explosive bolt that is arranged in an outer wall of the distribution chamber. Explosive bolts are inexpensive and prefabricated pyrotechnical units that can be attached in the distribution chamber with little effort.
Preferably, several second outflow openings are provided that are arranged in such a way that they discharge outflowing gas to the environment in a shear-neutral manner, that is to say, without any resultant force being generated. Consequently, the components of the airbag module and their attachments can be retained unchanged, since no high stresses occur.
In another embodiment, the second outflow opening is integrated into the pyrotechnical device. This offers the advantage that the requisite structural changes are largely concentrated in the pyrotechnical device, in other words, in a prefabricated add-on part that is additionally provided anyway. Only a few changes have to be made to the actual gas generator.
As an alternative, a membrane can be present that divides the distribution chamber into two areas, a first area containing the first outflow opening and a second area containing the second outflow opening. The pyrotechnical device destroys the membrane after it has been activated.
In this embodiment with a membrane, the pyrotechnical device is preferably arranged in the second area of the distribution chamber. In this manner, when the gas generator is triggered, the gas flow is not hindered as a rule, i.e. without activation of the pyrotechnical device.
In particular, the gas generator can be a tubular gas generator with a tube axis, the generator chamber and the distribution chamber being arranged axially behind one another. In this case, necessary structural changes to the gas generator can easily be made without this affecting other components of the airbag module.
Preferably, the distribution chamber is formed by a separate part attached to the generator chamber. In this case, the generator chamber, together with its appertaining parts (igniter, attachment elements, etc.), remains unchanged as the main component of the gas generator. Only the distribution chamber is changed in that it now also has openings for venting the generator gas into the environment, in addition to the outflow openings to the airbag.
In one embodiment, the gas generator is a cold gas generator, the generator chamber having a chamber filled with compressed gas. In another embodiment, the gas generator is a hot gas generator, the generator chamber having a combustion chamber. This shows the extensive possibilities for using the invention, irrespective of the type of generator used.
Advantageously, the gas generator according to the invention is accommodated and attached in a module housing of an airbag module, the distribution chamber being configured in such a way that a section of the distribution chamber having the second outflow opening extends through an opening in the module housing in order to discharge gas from the airbag module to the environment. This offers the advantage that gas to be vented is not released via the module housing but rather directly from the gas generator into the environment of the module.
In another embodiment, at least one attachment bolt is provided between the distribution chamber and the module housing in order to attach the gas generator to the module housing, the pyrotechnical device for releasing the second outflow opening being integrated into this attachment bolt. As a result, the number of components is kept low, which simplifies and speeds up the assembly of the airbag module.
Preferably, the shape of the distribution chamber and the cross sections of the first and second outflow openings are coordinated with each other in such a way that, when the pyrotechnical device is triggered, a gas mass flow into the airbag is established that amounts to between 20% and 80%, preferably about 50%, of the value achieved when the second outflow opening is closed. This shows that the minor structural changes to the gas generator allow a very good control of the gas mass flow.
a to c show top views of identical modules, each fitted with different gas generators;
a and b show two longitudinal sections through an airbag module according to the invention and a gas generator according to the invention in the first embodiment;
a and b show two longitudinal sections through an airbag module according to the invention and through a gas generator according to the invention in a second embodiment;
a and b show two longitudinal sections through an airbag module according to the invention and through a gas generator according to the invention in a third embodiment;
a and b show two longitudinal sections through an airbag module according to the invention and through a gas generator according to the invention in a fourth embodiment;
a and b show two partial sections through an airbag module according to the invention and through a gas generator according to the invention showing two variants of the gas generator in the fourth embodiment; and
The upper part of
a, like
a and 3b each show a section through a first embodiment of the gas generator 8 as well as through areas of the module housing 10 and through an airbag 24. The axial ends of the gas generator 8 extend through openings in the airbag 24 and in the module housing 10, so that the triggering unit 16 and the pyrotechnical device 18 are visible from outside of the module. The gas generator 8 is attached on one lengthwise side to the module housing 10 by means of the attachment bolts 20. The airbag 24 is clamped between the gas generator 8 and the module housing 10, the airbag 24 having cutouts at the attachment bolts 20.
The gas generator 8 includes a gas generator housing 25, defining the generator chamber 12 with the triggering unit 16 as well as the distribution chamber 14 with the pyrotechnical device 18. The generator chamber 12 and the distribution chamber 14 are formed by the gas generator housing 25, hence are part of the gas generator 8. The generator housing 25 can be manufactured in one piece or in several pieces being attached to one another later on. For example, the distribution chamber 14 is preferably a one-piece component of the gas generator 8. As an alternative, it is made up of one or more parts that are permanently attached, especially by means of welding, to the rest of the gas generator 8, for instance, to an outer wall of the generator chamber 12. First outflow openings 26 and second outflow openings 28 are provided in the distribution chamber 14, the first outflow openings 26 serving to convey gas into the interior of the airbag 24 and said second outflow openings 28 serving to vent gas from the airbag module into the environment. In
The pyrotechnical device 18 is arranged in the second area of the distribution chamber adjacent to the membrane 30. When the pyrotechnical device 18 is triggered, the membrane 30 is destroyed so that the second outflow openings 28 are exposed (
FIGS. 4 to 7 show additional embodiments of the gas generator 8 and of the airbag module. In general, the same applies that was mentioned for
a and 4b show a second embodiment of the gas generator 8 and the airbag module. Here, the difference from
The mode of operation of the gas generator 8 in a third embodiment according to
a and 6b show a fourth embodiment of the gas generator 8, which is very similar to the embodiments according to
The effect of the second outflow openings 28 is illustrated on the basis of a diagram in which the gas mass flow M into the airbag 24 is plotted over time t. Such curves depend, of course, on the shape of the distribution chamber 14 and on the cross sections of the first and second outflow openings 26, 28. Merely by way of an example, the applicable mass flow curve of an advantageous combination is plotted. The solid line indicates the gas mass flow into the airbag 24 if the second outflow openings 28 remain closed. If the second outflow openings 28 are opened at a point in time t1, then the mass flow M immediately drops to about 50% of the mass flow without the opening of the second outflow openings 28 (thick broken line). If the second outflow openings 28 are opened at the point in time t2, then the mass flow M drops to about 20% of the original mass flow M (thin broken line). Efforts are aimed at having cross sections and distribution chamber shapes with which, depending on the point in time when the second outflow openings 28 open, a gas mass flow into the airbag 24 is established that lies between 20% and 80% of the value achieved when the second outflow opening is closed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 049 554.0 | Oct 2005 | DE | national |
