DE4108857C1 - Cylindrical gas generator for inflating gas sack of impact protection unit - has combustion chamber with housing, propellant, ignition device and filter unit - Google Patents

Abstract

A cylindrical gas generator for inflating the gas sack of an impact protection unit for one or more occupants of a vehicle, esp. for the passengers, includes a combustion chamber with a surrounding housing, a propellant, an ignition device, and a filter unit which is connected to the combustion chamber via gas outlet openings. Downstream of the gas outlet opening is a pressure reducing cross section, in the filter unit region. An elastic and/or plastically deformable deformation element is located near the pressure reducing cross-section. ADVANTAGE - The gas generator is fully functional between -30 and +100 deg.C.

Description

The invention relates to a cylindrical gas generator for inflation the gas bag of an impact protection device for one or more occupants a vehicle, according to the preamble of claim 1.

There are practically all common types of propellant for gas generators a dependence of the burning rate on the outside temperature and in such a way that the burning rate with increasing outside temperature increases. Assuming fixed, predetermined geometries in the combustion chamber as well as in the flow channels, that the pressures and thus the mechanical load on the gas generator increase with increasing outside temperature. The burn-up time decreases, which in turn leads to a faster inflation of the gas bag, associated with a higher load of this protective element and with an increasing Sound pressure load on the occupants.

This makes it clear that high outside temperatures are more critical than low, especially because of the risk of gas generator fragmentation or individual parts thereof.

At low temperatures you may have the problem that the gas bag is not inflated fast enough.

From DE-PS 31 47 780 a tubular passenger gas generator is known which is provided with a valve-like pressure relief device is the temperature dependence of the inflation speed and to reduce the inflation pressure. There is one with increasing temperature more easily deformable, elastic cone part made of plastic, which at high temperature and high pressure an additional Flow path releases. This flow path leads from one of the filters downstream chamber from past the gas bag into the open. In this way  the inflation behavior is improved and the gas bag is relieved, relief of the gas generator itself, d. H. a reduction in risk fragmentation, but is not a given.

DE-AS 25 18 460 is a solution for driver and front passenger gas generators known in the regulation and limitation of the combustion chamber pressure the combustion chamber itself in one against the force of an elastic or plastically deformable element arranged displaceable container is. In cooperation with the open side of the container with a the combustion chamber pressure itself regulates the solid, opposite wall the combustion chamber outflow cross section. Such a solution is in the Practice, however, extremely problematic. The guidance of the sliding container on the one hand should be as precise as possible so that it does not tilt can occur. On the other hand, the danger increases with increasing accuracy of jamming - in operation - due to uneven deformation of the Container, various thermal expansion of the container and guide and - before start-up - due to corrosion, fretting corrosion etc. For reasons of space the displacement is relatively narrow, so that the exit cross-section change is limited. The flow resistance also remains the downstream cooling and filter device always same, so that at very high outside temperatures there is a strong pressure increase is expected in the gas generator.

Due to the unreliable mechanics and the flow design in the area the cooling and filter device is even the solution described particularly dangerous with regard to fragmentation.

A particularly difficult test prescribed by law for gas generators is the "bonfire test", in which the gas generator heated and burned on an open wood fire to self-ignition becomes. This is used to simulate the gas generator behavior at a Vehicle fire, although no fragmentation may occur here. Here  it should be noted that the high ignition temperatures of approx. 350-450 ° C the strength of the aluminum alloys often used for gas generator parts already drastically reduce.

In contrast, users of gas generators test, i.e. H. the module and Vehicle manufacturer, only at a temperature of -30 ° C, at room temperature as well as at a temperature of + 85 ° C. At these temperatures is the requirement of non-fragmentation without too much effort meet, although here also the cooling and filter functions checked will.

In view of the above test arrangements and in view of the Disadvantages of the solutions according to the prior art are the task the invention in a cylindrical gas generator with at least a filter device arranged essentially outside its housing and with a device for releasing at least one leading out of it To create flow path for pressure relief, which at Outside temperatures from around -30 ° C to around + 100 ° C fully functional is, in particular with regard to the filtering and cooling of the fuel gases, and which in the "bonfire test" certainly without any fragmentation burns.

This task is characterized by the features in the main claim solved.

The invention takes into account the fact that usually less Combustion chamber and its exit area as the filter itself mechanically and fluidically (pressure losses) particularly critical is, especially with increasing burning time and particle load. This applies all the more if - as in the present case - from cost-oriented and production-related reasons an essentially self-supporting filter is used without a supporting filter housing.  

Therefore, according to the invention, downstream of each filter device of the filter at least one by elastic or plastic deformation at least one deformation element, directly or indirectly Generable or releasable pressure relief cross-section that leads past the filter available. The deformation element or elements are like this dimensioned and preloaded so that - starting from the installed state - only deform at pressures which are at outside temperatures of occur significantly above + 100 ° C, e.g. B. in the "bonfire test". Here will at least some of the fuel gases are passed unfiltered from the gas generator, which, however, is irrelevant especially in the "bonfire test". Both mentioned user tests occur the protective elements according to the invention not in function, so that no restriction of the filter and cooling effect given is.

The sub-claims 2 to 5 have preferred configurations of the gas generator according to claim 1, the versions according to claim 2 and 3 are alternative to each other.

The invention will be explained in more detail below with reference to the drawings explained. A simplified representation shows:

Fig. 1 shows a partial longitudinal section through a gas generator having axially displaceable filter,

Fig. 2 shows a partial longitudinal section through the combustion chamber of a gas generator remote from the end with a radially deformable deformation element, and

Fig. 3 shows a cross section according to the course of 2 AA in Fig..

The housing 3 of the gas generator 1, which is only partially shown, surrounds the combustion chamber 4 with the propellant charge and the igniter (both not shown), the combustion chamber end wall 5 being provided with gas outlet openings 6 for the fuel gases generated. Since it is a gas generator version without a filter housing, the housing 3 ends in a support pin 7 connected to the combustion chamber end wall 5 for the filter device. The filter device with suspension can - as shown - be present on one side or symmetrically on both sides of the combustion chamber.

The gas deflecting ring 10 serves to initially guide the gases emerging from the combustion chamber end wall 5 radially inward away from the filter 11 in order to avoid short-circuit faults through the filter end on the combustion chamber side. Furthermore, the gas deflection ring 10 accommodates the filter end on the combustion chamber in a sealing and supporting manner in the idle state and in operation with normal pressures (see FIG. 1 below).

The at least largely self-supporting, hollow cylindrical filter 11 forms with the gas divider 13 an axially displaceable unit on the support pin 7 . The gas divider 13 , which is stepped several times in diameter, has several functions. It improves the flow design in the sense of a more uniform filter application over the filter length, it forms the dense wall of the flow channel opposite the combustion chamber end wall and it carries the end of the filter 11 facing away from the combustion chamber. Furthermore, in the area of its smallest diameter, the gas divider 13 forms an at least largely gas-tight sliding guide with the support pin 7 , additional sealing elements such as O-rings etc. possibly being present (not shown).

The representation below the center line shows the usual operating case with normal gas pressures, in which the fuel gas flow in its entirety is passed through the filter 11 . Under these conditions, the unit consisting of filter 11 and gas divider 13 is held in a position facing the combustion chamber via an axially preloaded deformation element, here a corrugated tube 18 , the gas deflection ring 10 forming the axial stop and the radial guide for the filter end on the combustion chamber side. The corrugated tube 18 is pretensioned by means of a nut 9 which interacts with a thread 8 on the support pin 7 . Instead of the corrugated tube 18 , of course, other deformation elements can be used, such as. B. disc springs, coil springs or non-metallic, rubber-elastic molded body. The corrugated tube 18 has the advantage, among other things, that it acts as an additional gas seal.

The position of the filter 11 and gas divider 13 shown below the center line is - apart from the normal operating case - also in the idle state, ie before commissioning, and under the conditions of the user tests mentioned at temperatures of -30 ° C, + 85 ° C and at room temperature . In other words, the prestressed deformation element brings about a quasi-rigid connection between the gas divider 13 and the trunnion 7 under these conditions.

The arrows shown in the figure without reference numerals indicate schematically the possible flow pattern during operation.

This is in normal operation as well as under the test conditions mentioned ensures that the entire fuel gas stream is filtered and cooled enters the gas bag.

Above the center line, the case is shown in FIG. 1 that, due to extremely high outside temperatures, the propellant burns off at a high rate of erosion with the generation of extreme gas pressures. This is the case with the "bonfire test", in which - as mentioned - the gas generator is burned on an open wood fire and checked for possible signs of fragmentation. Ultimately, this test is used to simulate the conditions in the event of a vehicle fire, and people in the vicinity must not be injured by gas generator parts accelerated as a result of fragmentation. It is obvious that the filter and cooling effect of the filter device is practically irrelevant in this case, since firstly it can be assumed that the gas bag has already been destroyed by the high ambient temperatures at the time the propellant is self-igniting, and secondly at this time People who are still in the vehicle are likely to be already dead or fatally injured. So it is only about the safety of people outside the vehicle, such as helpers or rescued vehicle occupants.

The invention takes these circumstances into account by operating at extreme Press part of the gas flow in the area of the filter device unfiltered and uncooled past the filter into the gas bag or into Free leads. As a result, the gas pressures and thus the mechanical Stress on critical components, especially the filter itself, is so high reduces the risk of fragmentation.

As shown in Fig. 1 above the center line, the filter 11 is displaced together with the gas divider 13 by the displacement s away from the combustion chamber 4 , whereby between the gas deflection ring 10 or the housing 3 and the combustion chamber end of the filter 11 Desired pressure relief cross section 16 is released. The corrugated tube 18 is pushed together elastically or plastically to a minimum remaining length and, together with the nut 9 , thus limits the maximum displacement path.

In general it can be said that a plastic deformation or even a Destruction (breakage, shearing, etc.) of the deformation element is accepted can, if the stop function is retained, because the The process of cross-section approval (pressure relief) is usually not must be reversible. A plastic deformation may also have that Advantage that the moving parts vibrate less, here longitudinal vibrations, tend.

Figs. 2 and 3 show a comparison with FIG. 1 a constructive different embodiment of the invention, wherein for simplicity, only the relevant region of the gas generator 2, namely the combustion chamber distal end is shown.

The filter 12 and the gas divider 14 are firmly connected to the housing of the gas generator 2 , ie they cannot be axially displaced. Instead, the diameter of the cylindrical region 15 of the gas divider 14 , which is the largest radially inside the filter 12 , is provided with permanently molded, pressure-relief cross-sections 17 which are evenly distributed over its circumference and which are released at particularly high gas pressures in the filter region. The valve function is carried out by a deformation ring 19 which bears radially from the inside under prestress.

Based on FIG. 1, the representation in FIGS. 2 and 3 is chosen such that the state with pressure relief is shown above the center line and the normal state is shown below the center line. As can be seen in FIG. 3, the deformation ring 19 consists of partially cylindrical and inwardly corrugated areas, the former being necessary for sealing or releasing the pressure relief cross sections 17 , the latter for the radial deformability. The part-cylindrical regions are adapted to the inner diameter D of the cylindrical region 15 of the gas divider 14 . Instead of the simple corrugation shown between the partially cylindrical regions, a multiple corrugation can also be used. It will also be expedient to provide protection against the axial displacement of the deformation ring 19 from the gas divider 14 (not shown).

In general, the deformation element can consist of several parts with functional Separation of sealing and prestressing must be composed, e.g. B. from valve elements and springs.

The principle common to all possible designs is that the Deformation of at least one prestressed deformation element directly or indirectly at least one pressure relief cross section leading past the filter is generated or released.

Claims (5)

1.Cylindrical gas generator for inflating the gas bag of an impact protection device for one or more occupants of a vehicle, in particular for the passenger or passengers of a motor vehicle, with a housing enclosing a combustion chamber with a propellant, with an igniter for the propellant, with at least one in an axial extension of the Combustion chamber attached to the housing filter device which is connected or connectable to the combustion chamber via gas outlet openings in the housing and comprises at least one hollow cylindrical filter, through which the combustion gases flow essentially radially before exiting into the gas bag, and with a device for releasing at least one from the gas generator leading flow path in the event of combustion with high gas pressure at high outside temperatures, characterized in that at least downstream of the gas outlet openings ( 6 ) of the combustion chamber ( 4 ) in the area of each filter device ( 11 or 12 ) ens a pressure relief cross-section ( 16 or 17 ) that can be passed by the filter ( 11 or 12 ) by adjoining components ( 10 and 11 or 15 and 19 ) and at least one elastically and / or plastically deformable deformation element ( 18 or 19 ) indirect or immediate release of the pressure relief cross-section ( 16 or 17 ) are available. 2. Gas generator according to claim 1, having at least one combustion chamber end wall provided with gas outlet openings, having a gas deflecting ring concentrating the combustion gases towards the center, receiving the combustion chamber end of the filter, and having a gas-tight, essentially rotationally symmetrical, connected to the end of the filter facing away from the combustion chamber and connected to the combustion chamber end wall Supported gas divider, characterized in that the gas divider ( 13 ) is axially displaceable and gas-tight on a central guide (support pin 7 ) connected to the combustion chamber end wall ( 5 ) against the force of a prestressed, axially deformable deformation element ( 18 ), and that Maximum displacement (s) of the gas divider ( 13 ) and the filter ( 11 ) connected to it is so large that at high gas pressure between the gas deflection ring ( 10 ) and the combustion chamber end face of the filter ( 11 ) the desired pressure relief cross section ( 16 ) is available . 3. Gas generator according to claim 1, with at least one combustion chamber end wall provided with gas outlet openings and with a gas-tight, substantially rotationally symmetrical, multi-step in diameter, supporting the end of the filter facing away from the combustion chamber and supported on the combustion chamber end wall, characterized in that a combustion chamber remote, with radial Distance within the filter ( 12 ), cylindrical region ( 15 ) of the gas divider ( 14 ) is provided with at least two radially oriented pressure relief cross-sections ( 17 ) evenly distributed over its circumference, and that a prestressed, at least radially deformable deformation element ( 19 ) in depressurized state or at normal gas pressure radially sealing from the inside to the pressure relief cross-sections ( 17 ), but is deformed at high gas pressure in such a way that fuel gases can escape between the deformation element ( 19 ) and the gas divider ( 14 ). 4. Gas generator according to claim 2, characterized in that the axially deformable deformation element is designed as a corrugated tube ( 18 ). 5. Gas generator according to claim 3, characterized in that the at least radially deformable deformation element as a deformation ring ( 19 ) with partially cylindrical in the installed state, lying on the same diameter (D) and with areas arranged between them, lying within said diameter (D), corrugated areas, the number of partially cylindrical and corrugated areas each corresponding to the number of pressure relief cross sections ( 17 ) in the gas divider ( 14 ).