Propulsive Device for restraint systems in motor vehicles.

p0001The invention relates to a driving device for restraint systems in vehicles, comprising a pyrotechnic gas generator, the gases act on a working chamber.

p0002Such drive devices are required for example in seat-belt pretensioners, as are known from DE-OS 31 31 637th

p0003Pyrotechnic gas generators as power sources for driving devices of this type particularly suitable because they are able to supply, within a short period of a few milliseconds which require quantities of gas under extremely high pressure. These high pressures must the working chamber of the device, such as a cylinder in which a piston slides, withstand. The prevailing in motor vehicle pursuit lightweight construction to reduce weight and material savings will find its limit on the minimum requirements for the mechanical strength of the device.

p0004Even higher demands on the mechanical strength caused by the fact that the risk of bursting or flying parts should be even with a self-ignition of the gas generator due to an exceptional heating, especially in case of fire of the motor vehicle, excluded. The of a gas generator of energy released is in fact at temperatures in the range of the auto-ignition temperature is much greater than at normal operating temperatures, the upper limit is about 80 °. Moreover, steps up the components of a device in lightweight construction, in particular aluminum or aluminum alloys produced when heated to the auto-ignition temperature of the gas generator, for example, about 180 ° C, leads to a considerable reduction in mechanical strength. Special vulnerabilities are bolted, which meet at normal operating temperatures but the demands placed on them in terms of mechanical strength well.

p0005The invention has the object of developing a driving device of the aforementioned kind such that with a basic design and dimensioning, which is unchanged from one designed for moderate operating temperatures embodiment, each hazard is also excluded from bursting or flying debris when the device is heated up to the spontaneous combustion temperature of the gas generator Tempe.

p0006This object is achieved in a generic drive device according to the invention that the working chamber comprises an outwardly leading relief path which is closed by a closure member of a material that at a temperature above the operating temperature range of the gas generator temperature that is no greater than the auto-ignition temperature of the gas generator softens at least to such an extent that the closure element on ignition of the gas generator the relief path releasing, at temperatures within the operating temperature range of the gas generator, however, has such mechanical strength that the relief path remains sealed by the closure element in gas action. This inventive configuration of the driving device is ensured that, for a self-ignition of the gas generator, for example due to a fire of the motor vehicle, which then under particularly high pressure gases generated can largely escape via the relief path. A charging of the working chamber with extremely high gas pressure is therefore avoided. So it must be placed no higher demands on the mechanical strength of the working chamber, so that the desired lightweight construction is not excluded by the requirement that even with a self-ignition of the gas generator is no danger to start from the drive device. As long as the heating of the drive device remains within the limits of the normal operating temperature range, for example at a maximum of 80 ° C, however, the discharge channel by the closure element remains securely closed, so that the function of the driving device is not impaired.

p0007When the upper limit of the operating temperature range of the gas generator lies at about 80 ° C, so should the softening temperature of the material from which the closure member, are from about 120 ° C to 130 ° C; In general, to consist almost the same or slightly larger temperature difference between the softening temperature of the material from which the closure element, and the auto-ignition temperature of the gas generator as between softening temperature and the upper limit of the operating temperature range of the gas generator. In this way it is achieved that the closure element is not losing the one hand, within the normal operating temperature range of strength, on the other hand when it reaches the self-ignition temperature, the softening of the closure element is already so far advanced that a release of the relief channel is ensured with high security.

p0008The closure member is preferably received in a form-fitting manner the relief path-forming channel. A particularly high load of the closure element arises when facing one of the gas action, having widened base surface, is thus designed especially frustoconical, and its tightness is conveyed in the channel under the action of the gas action by wedging action. The closure member then forming an outwardly leading opening of the working chamber occlusive plug. This stopper can also be formed by filling the aperture, whereby the manufacture is simplified.

p0009Particularly advantageously, the invention is directed to the linear drive of a belt-tightening means is applicable, the working chamber is formed by a cylinder in which a piston is slidably by pressurizing one of its faces. The cylinder can then be made of aluminum and be bolted to the gas generator receiving base, although such a construction may not meet the extremely high loads that would occur in a spontaneous combustion of the gas generator due to excessive heating of the device, if no relief path would exist ,

p0010In such an application of the relief path between the inner wall of the cylinder and the piston can be formed, in particular in the form of a ring surrounding the outer surface of the piston which is positively connected to the piston. Such an embodiment requires only minor modifications to an existing design facilities thereof. With the inventively provided relief path

p0011An equally feasible with little effort modification of an existing structure is possible in embodiments in which the cylinder is connected to the gas generator via an angled channel. The relief path is then used as formed by the closure element closed bore in the extension of one of the angled branches of the channel.

p0012The material from which the closure element is formed may be metallic or synthetic. Are particularly expedient eutectic alloys, in particular an alloy of 55.5 wt .-% Bi and 44.5 wt .-% Pb. The melting temperature of such a eutectic alloy is 124 ° C.

p0013Particularly suitable plastics are those which retain up to its softening a high mechanical strength, which is the case in particular for polypropylene, whose softening temperature is about 130 ° C or slightly higher.

p0014Further features and advantages of the invention will become apparent from the following description of several embodiments and from the drawing, which is incorporated by reference. In the drawings:<ul><li>Figure 1 shows a schematic longitudinal section of an embodiment form in which the drive device forms a piston / cylinder drive mechanism for a seat belt tightening means.</li><li>Fig. 2 shows a variant of this embodiment;</li><li>Figure 3 is a closure member and for receiving the same particular opening prior to assembly of the closure element. and</li><li>Fig. 4 shows the same closure member and the same opening after assembly of the closure member.</li></ul>

p0015The drive device shown in Figure 1 for a seat belt tightening means comprises a generally L-shaped housing 10 in whose one leg 12, a receiving bore is formed for a pyrotechnic gas generator 14 which extends in a channel 16 to the other, bent at right angles leg 18 continues and passes into a channel formed therein 20th In this channel 20 opens a channel 22, which runs parallel to the channel 16 and passes into the interior of a cylinder 24th This interior of the cylinder 24 forms a working chamber in which a piston 26 is slidably received. In the piston 26, the end of a traction cable 28 is attached. This pull rope 28 engages at the circumference of a pulley, which translates the linear motion of the piston 26 into a rotational movement, which is transmitted to the belt reel of a belt retractor for tightening Mung of the webbing. The housing 10 is equipped with a mounting flange 30th

p0016The gas generator 14 has an electric igniter via a connecting cable 32 to a tripping connected seelektronik.

p0017Both the housing 10 and the cylinder 24 are made of a lightweight material of lower strength, in particular aluminum. The mounting of the cylinder 24 on the housing 10 is effected by a threaded connection, by the externally threaded end of the cylinder 24 is screwed into an internally threaded extension of the channel 22nd

p0018In normal operation of the drive device of the pyrotechnic gas generator 14 is ignited by means of its electrical igniter by applying a trigger pulse through the cable 32, whereupon generated under high pressure gases through the channels 16, 18, 20 and 22 act on the end face of the piston 26 and the latter in the chamber vortrei ben within the cylinder 24 until it is braked in a constriction at the end of the cylinder 24th

p0019To avoid any risk of bursting or flying parts in excessive heating of the device in which the gas generator 14 reaches its autoignition temperature, the device is equipped with a relief path, but which is only released when a temperature is reached, the well above the limit of the normal operating temperature range. This relief path is formed by an extension of the channel 20th This extension of the channel 20 forms an opening in the housing 10 which is closed by a closure member 34th The closure member 34 is seated in a form-fitting the end of the channel 20. In the embodiment shown, the positive engagement is achieved by an outer thread of the closure element 34, which is screwed into a corresponding internal thread on the mouth of the channel. The closure member 34 consists of a material having at a heating to temperatures within the operating temperature range of the device, for example to 80 ° C, a sufficient mechanical strength to withstand the gas pressure during normal operation of the gas generator fourteenth On the other hand, the material of which the closure element is 34, a melting or softening point which is below the autoignition temperature of the gas generator 14, for example at about 120 to 140 ° C, when the auto-ignition Tempe is temperature at about 180 ° C.

p0020A suitable material for the closure element 34 is a eutectic alloy of 55.5 wt .-% Bi, and 44.5 wt .-% Pb. This alloy has a melting point of about 124 ° C.

p0021Also suitable are plastics that have a softening point in the range of about 120 ° to 150 ° C. Particularly suitable is polypropylene having a melting point of about 130 ° to 150 ° C.

p0022In the embodiment shown in Figure 2, the closure element of the discharge channel is formed by a ring 38 which surrounds the lateral surface of the piston 26 and is positively connected thereto by an integrally formed rib 40th Which the closure member 38 forming the ring is therefore arranged between the piston 26 and the inner surface of the cylinder 24th

p0023In the embodiment shown in Figures 3 and 4, the closure member 42 forms a truncated cone-shaped plug which is inserted into a correspondingly shaped opening 44 of the housing 10 so that its large base surface facing the interior of the housing 10th After insertion of the closure member 42 in the opening 44 an interference fit is produced by caulking of the tapered end of the truncated cone-shaped closure element 42; This state is shown in FIG. 4

p0024The fastener elements 38 and 42 can be manufactured from the same material as the closure element 34. A simple manufacture of the plug-shaped closing element 34 or 42 is achieved in that the receiving opening is sealed for this closure member by casting, in particular by means of a eutectic alloy.