Device containing pyrotechnic material and method of manufacturing said device

Abstract

The present invention relates to a device containing pyrotechnic material, having a housing surrounding the pyrotechnic material, the device being wherein the housing is formed entirely from glass and contains at least one metal duct having a spark gap or a heating wire.

Description

1. The present invention relates to a device containing pyrotechnic material, comprising a housing surrounding the pyrotechnic material, and a method of manufacturing the device. In particular, the invention relates to a gas generator for a safety arrangement in motor vehicles or an igniter for such a gas generator.

BACKGROUND OF THE INVENTION

2. The gas generators and igniters currently on the market generally have a housing of stainless steel, aluminum or plastic. In fact in the igniters for gas generators, a high expenditure is necessary in order to produce these in a fluid-tight and gas-tight construction. In most cases, the metal ducts for the connecting cables of the igniters are cast integral into a metal ring with glass and the metal ring is connected by means of a welding process with the remaining housing parts of the igniter.

3. Even an employment of plastic housings can not always ensure the gas-tight and fluid-tight construction of the igniter. Owing to the plurality of the required process steps, the production of the known igniters is additionally extremely cost-intensive.

SUMMARY OF THE INVENTION

4. The present invention provides a device containing pyrotechnic material, in particular an igniter for a gas generator which is absolutely gas-tight and fluid-tight, has a lower weight compared with the known igniters and owing to the use of a continuous manufacturing process can be produced at a more favorable cost. According to the invention, for this a device containing pyrotechnic material is provided, comprising a housing surrounding the pyrotechnic material, which device is wherein the housing is formed from glass and contains at least one metal duct with a heating wire or a spark gap.

5. The pyrotechnic material can be solid, liquid or gaseous. Preferably the device is an igniter for a gas generator for use in a safety device for motor vehicles, which contains one or more heating wires or a spark gap for igniting the pyrotechnic material. The pyrotechnic material can comprise a primary charge and a booster charge. The primary charge takes up in an optimum manner the thermal energy arising through the activation of the igniter by means of a current impulse and ignites the booster charge. The booster charge provides the necessary amount of energy-rich hot particles to ignite the propellant usually contained in the gas generator.

6. A particularly preferred embodiment of the device according to the invention contains an arrangement by which in the case of an undesired thermal action from the exterior, for example when the vehicle catches fire, an opening is exposed and thereby a controlled outflow can be ensured of the gas released by the self-ignition of the pyrotechnic material. This arrangement preferably comprises a material which is crystalline or liquid at room temperature and is introduced at a suitable point into the glass housing of the device. The crystalline or liquid material alters its structure, its physical condition or its volume below the self-ignition temperature of the pyrotechnic material in such a way that when the undesired thermal action from the exterior occurs, the arrangement exposes the opening in the housing of the device which is closed by the arrangement.

7. The arrangement can comprise in particular an opening formed in the glass housing of the device, the opening being closed by a sealing means which may be formed particularly preferably from a low-melting-point metal alloy. The sealing means may further be a liquid contained in a closed glass container, the glass container being introduced in the opening and integrally connected with the glass housing.

8. The device according to the invention can also be a gas generator for a safety arrangement in vehicles, which generator can be used in particular in belt tensioner units or airbag modules.

9. A further subject matter of the invention is a method of manufacturing a device containing a pyrotechnic material, the method comprising the following steps:

10. (a) providing a glass bulb having at least one opening;

11. (b) introducing the pyrotechnic material and the at least one metal duct with the spark gap or the heating wire into the glass bulb;

12. (c) closing the at least one opening of the glass bulb forming a glass housing completely surrounding the pyrotechnic material and containing the metal duct.

13. In a preferred embodiment of the method according to the invention, first the metal duct with the spark gap or the heating wire can be introduced into the glass bulb through a first opening, the glass bulb can be heated in the region of the metal duct up to softening of the glass material and be closed in a gas-tight and fluid-tight manner for example by pressing or squeezing the softened glass. Glass bulbs having melted-in metal ducts and the associated heating wires or spark gaps may also be utilized in the form of already prefabricated units. Thereafter, the pyrotechnic material is introduced into the glass bulb through a further opening and this opening is likewise closed in a gas-tight and fluid-tight manner. The closing may be done for example by sealingly melting, pressing or squeezing. The glass bulb is preferably heated up to softening near the region of the opening and is pulled apart so as to produce a reduction in cross-section of the opening and to facilitate the subsequent process of sealingly melting or squeezing off. In a particularly preferred embodiment the glass bulb already has a narrowed cross-section in the region of the further opening.

14. The pyrotechnic material may be cooled beforehand in order to avoid self-ignition. However, selecting a suitable distance between the region to be heated and the pyrotechnic material may make the cooling of the pyrotechnic material unnecessary because of the low thermal conductivity of glass. The device thus produced comprises an integral glass housing which completely surrounds the pyrotechnic material and into which the metal ducts for the connecting cables of the igniter are melted in like in the known halogen bulbs. The device is therefore absolutely gas-tight and fluid-tight.

15. In a further embodiment of the method according to the invention, the spark gap or the heating wire is surrounded by at least part of the pyrotechnic material, for example in the form of a squib containing the primary charge. The metal duct with the spark gap or the heating wire and the part of the pyrotechnic material surrounding the spark gap or the heating wire is then introduced into a tubular glass bulb and the glass bulb is closed in the region of the metal duct in the manner as described above. A self-ignition of the pyrotechnic material is avoided preferably by suitably selecting the distance between the pyrotechnic material and the heated area of the opening. If required, additional pyrotechnic material may be supplied to the glass bulb through a further opening and the opening may thereafter be closed by sealingly melting, pressing or squeezing, as described above.

16. It is furthermore possible to introduce first the pyrotechnic material and thereafter the metal duct with the spark gap or the heating wire into the glass bulb provided with an opening and then to close the opening in the region of the metal duct in the manner as described above. For this purpose, for example a glass bulb is provided, which is filled with the pyrotechnic material. Then the metal ducts, equipped with a heating wire or a spark gap, for the connecting cables are introduced into the glass bulb. In this case as well, the heating wire or the spark gap can already be surrounded by a squib containing the primary charge. Thereafter, the glass bulb containing the pyrotechnic material may be cooled intensively by means of liquid air or liquid nitrogen and the glass bulb may be closed by melting. The cooling step may be dispensed with if a suitable distance is kept between the pyrotechnic material and the heated area. This method, too, ensures a totally gas-tight and fluid-tight connection of the components of the igniter according to the invention.

17. If an acceleration sensor arranged in a vehicle detects an accident, the igniter connected electrically with the sensor is activated. The current impulse originating from the sensor causes a burning through of the heating wire or the jumping of a spark in the spark gap. Thereby, the pyrotechnic material or preferably the primary charge surrounding the heating wire is ignited. This primary charge in turn ignites the booster charge contained in the glass bulb. The ignition of the primary charge and/or of the booster charge causes a distinct pressure increase to occur inside the glass bulb, which causes the latter to burst. In this way, the hot particles released by the burning of the booster charge can strike onto a pyrotechnic propellant contained in the gas generator and can cause it to ignite.

18. The same mode of operation occurs if, instead of the igniter, the gas generator is constructed according to the invention with a glass housing. In this case, the ignition of the pyrotechnic material contained in the gas generator causes a pressure increase which causes the gas generator housing to burst. The hot gases produced by the burning of the pyrotechnic material are thus released and can actuate the safety arrangement, for example a belt tensioner or airbag.

BRIEF DESCRIPTION OF THE DRAWINGS

19. Advantageous embodiments of the invention will be apparent from the following description, in which reference is made to the enclosed drawings in which:

20. FIG. 1 is a diagrammatic view of an igniter according to the invention;

21. FIG. 2 is a cross-sectional view of an igniter according to the invention;

22. FIG. 3 shows a gas generator according to the invention;

23. FIG. 4 shows an igniter with an arrangement for exposing an opening;

24. FIG. 5 shows a gas generator with an arrangement for exposing an opening; and

25. FIG. 6 is a cross-sectional view of a gas generator with an igniter according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

26. The igniter shown in FIGS. 1 and 2 comprises a housing 10 of glass. Metal ducts 14 are melted into the glass bulb or glass housing 10 in a gas-tight and fluid-tight manner. At the end of the metal ducts projecting into the housing, a heating wire or a spark gap 16 is arranged. The heating wire or the spark gap 16 is surrounded by a primary charge 18. In the housing in addition a booster charge 20 can also be arranged, which receives and boosts the energy released by the primary charge 18 in the case of activation of the igniter.

27. If the igniter is activated by a current impulse originating from an acceleration sensor (not shown here), the heating wire or the spark gap 16 firstly ignites the primary charge 18 which in turn causes the burning of the booster charge 20. Through the burning of the booster charge 20 and/or of the primary charge 18, a pressure increase occurs in the housing 10. Through this pressure increase, the housing 10 bursts and releases the energy-rich, hot particles formed by the burning of the booster charge.

28. The gas generator illustrated in FIG. 3 basically has the same structure as the igniter shown in FIGS. 1 and 2. The housing 10 of the gas generator is likewise formed from glass. Metal ducts 14 are melted into the glass bulb or glass housing 10 in a gas-tight and fluid-tight manner, which at their end projecting into the gas generator have a heating wire or a spark gap 16. The heating wire or the spark gap 16 are surrounded by a squib 22 which can contain a primary charge and also in addition a booster charge (not shown here). In addition a propellant 24 is introduced into the glass housing 10 of the gas generator, the activation of which propellant 24 leads to a bursting of the glass housing 10 and hence to a release of the hot gases formed by the burning of the propellant 24. By means of these hot gases, a safety arrangement, for example a belt tensioner unit or an airbag module, can be actuated.

29. FIG. 4 shows an igniter which basically has the same structure as the igniter illustrated in FIGS. 1 and 2. In the embodiment illustrated here, an opening 26 is provided in the igniter housing 10 formed from glass, which opening 26 is closed by a sealing means 28. The sealing means 28 has the characteristic that with an action of heat from the exterior, below the self-ignition temperature of the pyrotechnic material introduced into the igniter, for example of the primary charge 18 or of the booster charge 20, it alters its structure, its physical condition or its volume and thereby exposes the opening 26. As sealing means, for example a low-melting-point metal alloy can be used. The exposing of the opening ensures that the gases developing as a result of a self-ignition of the pyrotechnic material can flow away in a controlled manner.

30. The gas generator shown in FIG. 5 likewise has the opening 26 provided in the housing 10 formed from glass. As described above, this opening is closed by a sealing means 28, for example a low-melting-point metal alloy. The opening 26 or the sealing means 28 can be arranged at any desired point on the housing 10. It is also conceivable that a thermal action from the exterior and the change to the structure, the physical condition or the volume of the sealing means connected therewith, leads not only to an exposing of the opening 26 but also to a partial destruction of the housing 10. Thereby, the surface area of the opening available for the outflow of the gas produced as a result of the self-ignition of the propellant is enlarged. In the housing 10 also a plurality of openings 26, closed by the sealing means 28, can be provided.

31. Finally, FIG. 6 shows an example for application of a gas generator including an igniter according to the invention inserted in the gas generator. The gas generator illustrated here comprises a housing 30 formed of conventional materials such as aluminum or steel and a base part 32 closing off the housing. The base part may be made of plastic. In an upper portion of the base part 32 facing the interior of the housing 30, an O-ring 34 is arranged which holds the housing 30 in position in the nature of a latch. Further latching means may be provided on the outer periphery of the base part 32 for holding the housing in place.

32. Further, an igniter according to the invention is inserted in the upper part of the base part 32, between the O-ring 34. This igniter has the same structure as the igniter shown in FIGS. 1 and 2, i.e. it consists of a housing 10 which is entirely formed from glass and has metal ducts 14 melted into it in a gas-tight and fluid-tight manner. The metal ducts 14 comprise a heating wire 16 at their ends projecting into the glass housing 10 of the igniter. The heating wire may also be replaced by a spark gap in the known manner. The heating wire 16 is surrounded by a primary charge 18 which in turn is in contact with a booster charge 20. At their ends emerging from the glass housing 10 the metal ducts 14 are connected with the connecting cables 36 for the igniter.

33. The gas generator illustrated in FIG. 6 may be used in belt tensioner units, for example. When the igniter is activated via the igniter connecting cables 36, the heating wire 16 will fuse and thus ignite the pyrotechnic material 18, 20 contained in the glass housing 10 of the igniter. The increase in pressure brought about by the burning of the pyrotechnic material 18, 20 causes the glass bulb of the igniter to burst and releases the housing 30 of the gas generator from its locked position. The displacement of the housing 30 may be transferred in a known manner to a linear drive for a belt tensioner via a shoulder 38 arranged on the outer periphery of the housing 30.

34. Use of the igniter illustrated here is however not limited to gas generators for belt tensioner units. Rather, the igniter according to the invention may be utilized in any one of the known gas generators for safety arrangements, for instance in gas generators for driver's side impact protective device, front passenger impact protective devices and side impact protective devices.

35. To produce the device according to the invention or the igniter according to the invention, preferably a glass tube is provided which has a first opening and a second opening located opposite the first opening. The metal ducts, which preferably consist of tungsten or a tungsten alloy, are then introduced into the glass tube through the first opening with the heating wire or forming a spark gap, and the glass tube is heated in the region of the first opening until the glass softens, and is pressed so as to melt the metal ducts into the glass tube in a gas-tight and fluid-tight manner. The glass tube including the metal ducts melted into it may also be provided as a prefabricated component, such as is known, for example, from the production of halogen bulbs.

36. When the glass tube or glass bulb containing the metal ducts has been produced, the pyrotechnic material is introduced into the glass bulb through the second opening. The introduction of the pyrotechnic material may be performed in a plurality of steps which may be interrupted by drying stages. In this way it is also possible to introduce different pyrotechnic materials and to make the characteristics of the device suitable for any specifically desired purpose of application. Finally, the glass bulb containing the pyrotechnic material is sealingly melted in the region of the second opening. Preferably, the glass bulb already has a narrowed cross-section in this region, so that the step of sealingly melting may be effected by heating and pulling the glass bulb apart in the region of the narrowed cross-section. When proceeding in this manner, a cooling of the remaining portions of the glass bulb or of the pyrotechnic material may be done without due to the poor thermal conductivity of glass.

37. The igniter according to the invention ensures that the pyrotechnic material contained inside it is sealed in an absolutely gas-tight and fluid-tight manner and thus increases the functional reliability of the particular gas generator or safety arrangement concerned. At the same time, the application of a simplified and continuous manufacturing method allows a production of the igniter according to the invention at a favorable cost.

Claims

1. A device containing a pyrotechnic material, comprising a housing surrounding the pyrotechnic material, wherein the housing is formed entirely from glass, the housing containing at least one metal duct comprising a spark gap or a heating wire.

2. The device according to claim 1, wherein the device is an igniter for a gas generator.

3. The device according to claim 2, wherein the heating wire or the spark gap is connected with the pyrotechnic material.

4. The device according to claim 2, wherein the pyrotechnic material comprises a primary charge and a booster charge.

5. The device according to claim 1, wherein the device is a gas generator for a safety arrangement in motor vehicles.

6. The device according to claim 5, wherein the safety arrangement is a belt tensioner unit or an airbag module.

7. The device according to claim 1, wherein the pyrotechnic material is solid, liquid or gaseous.

8. The device according to claim 1, wherein the housing has at least one opening which is closed by a sealing means, the sealing means altering its physical condition, its structure or its volume as a result of an action of heat from the exterior below the self-ignition temperature of the pyrotechnic material in such a way that the opening is exposed.

9. The device according to claim 8, wherein the sealing means is a low-melting-point metal alloy or a liquid contained in a closed glass container, the glass container being introduced into the opening.

10. A method of manufacturing a device containing a pyrotechnic material, wherein the method comprises the steps of: (a) providing a glass bulb having at least one opening; (b) introducing the pyrotechnic material and at least one metal duct comprising a spark gap or a heating wire into the glass bulb; (c) closing the opening of the glass bulb forming a glass housing completely surrounding the pyrotechnic material and containing the metal duct comprising the spark gap or the heating wire.

11. The method according to claim 10, wherein the glass bulb is heated in the region of the opening until the glass softens, and the opening is closed by sealingly melting or pressing.

12. The method according to claim 11, wherein the pyrotechnic material is cooled during heating.

13. The method according to claim 11, wherein the heated area of the glass bulb is arranged at a distance from the pyrotechnic material, the distance being selected such that a cooling of the pyrotechnic material may be dispensed with.

14. The method according to claim 10, wherein the glass bulb has a narrowed cross-section in the region of the opening.

15. The method according to claim 14, wherein the glass bulb is heated, pulled apart and sealingly melted in the region of the narrowed cross-sectional portion.

16. The method according to claim 10, wherein prior to introducing the pyrotechnic material, the metal duct comprising the spark gap or the heating wire is introduced into the glass bulb and the glass bulb is closed in the region of the metal duct.

17. The method according to claim 10, wherein at least part of the pyrotechnic material surrounds the spark gap or the heating wire, the metal duct comprising the spark gap or the heating wire and the part of the pyrotechnic material surrounding the spark gap or the heating wire is introduced into the glass bulb and the glass bulb is closed in the region of the metal duct.

18. The method according to claim 10, wherein the pyrotechnic material is introduced into the glass bulb and wherein subsequently the metal duct comprising the spark gap or the heating wire is introduced into the glass bulb and the glass bulb is closed in the region of the metal duct.

19. The method according to claim 10, wherein the glass bulb is a glass tube having a first opening and a second opening located opposite the first opening, wherein the metal duct comprising the spark gap or the heating wire is introduced into the glass tube through the first opening and the glass tube, in the region of the first opening, is heated up to softening and closed and wherein subsequently the pyrotechnic material is introduced into the glass tube through the second opening and the glass tube, in the region of the second opening, is heated up to softening and closed.

20. The method according to claim 19, wherein the narrowed cross-sectional portion is arranged in the region of the second opening.

21. The method according to claim 19, wherein the glass bulb obtainable by introducing the metal ducts and closing the first opening is provided as a prefabricated component.

22. The method according to claim 10, wherein the device containing the pyrotechnic material is an igniter in a gas generator for a safety arrangement in motor vehicles.