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]    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]    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]    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]    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]    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]    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]    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]    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]    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]    10. (a) providing a glass bulb having at least one opening;  
           [11]    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]    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]    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]    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]    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]    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]    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]    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]    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]    20.FIG. 1 is a diagrammatic view of an igniter according to the invention;  
         [21]    21.FIG. 2 is a cross-sectional view of an igniter according to the invention;  
         [22]    22.FIG. 3 shows a gas generator according to the invention;  
         [23]    23.FIG. 4 shows an igniter with an arrangement for exposing an opening;  
         [24]    24.FIG. 5 shows a gas generator with an arrangement for exposing an opening; and  
         [25]    25.FIG. 6 is a cross-sectional view of a gas generator with an igniter according to the invention.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [26]    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]    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]    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]    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]    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]    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]    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]    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]    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&#39;s side impact protective device, front passenger impact protective devices and side impact protective devices.  
         [35]    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]    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]    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.