Abstract:
The invention relates to gas generator comprising an outer housing made of plastic, in which a pyrotechnic propellant charge and an igniter having its own igniter housing are accommodated. The igniter housing consists at least partially of plastic and is welded with the outer housing.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a gas generator.  
         BACKGROUND OF THE INVENTION  
         [0002]    Gas generators with an outer housing made of plastic have already been proposed and tested. In an outer housing of this type, there may be accommodated a pyrotechnic propellant charge and an igniter having its own igniter housing. It is an aim of the invention to provide a gas generator in which the sealing of the igniter in the plastic housing can be carried out in a simple manner so as to prevent the entry of moisture.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    This is achieved in a gas generator which comprises an outer housing made of plastic, in which a pyrotechnic propellant charge and an igniter having its own igniter housing are accommodated. The igniter housing consists at least partially of plastic and is welded with the outer housing. The welding on of the igniter took place hitherto always only via metallic sections thereof, but not via sections of plastic. Through the invention, it becomes possible to unify the connection of the individual parts in the production of the gas generator by the welding of plastic being provided exclusively. Thus the igniter, which is usually ordered as a separately delivered part, can be simply welded into a housing part, and the housing, in so far as it consists of several parts, is then likewise closed by welding. Through the welding of the plastic, connections can be realized which are gas-tight and are protected from the entry of moisture, without the intercalation of additional sealing elements.  
           [0004]    According to the preferred embodiment, the welding is an ultrasonic welding, i.e. a very favorably priced method.  
           [0005]    Furthermore, the igniter preferably has electric connecting lines which extend through at least one opening in the gas generator outer housing. The igniter housing seals the opening after welding, so that no moisture can penetrate into the interior of the gas generator and no gas can emerge via the opening on activation of the gas generator. The igniter, more precisely the section of the igniter which is made of plastic and is welded to the outer housing, therefore has a dual function, because it also serves as closure for the opening for the passage of the connecting lines. A sealing of the openings by potting, as was always proposed hitherto in the prior art, can be dispensed with.  
           [0006]    The outer housing preferably has a cup-shaped receiving part for the propellant charge and a cover to which the igniter is welded. The receiving part and the cover are likewise welded to each other, so that the same type of connection is selected.  
           [0007]    A radial gap between the receiving part and the cover can be provided, into which a projection of the igniter protrudes, whereby the latter is additionally secured in position. Possibly, this securing in position can absorb additional forces, so that the weld seam igniter/outer housing does not have to receive the entire mechanical stress.  
           [0008]    A particularly simple embodiment is distinguished in that contact sleeves are embedded in the cover, the igniter being provided with contact pins that are introduced into the contact sleeves. The contact sleeves are in addition preferably connected with connecting cables on their outer ends. Thus, for example, a simple electrical contacting can be achieved in that the contact sleeves, embedded into the cover by injection-molding or potting, together with the connecting lines and the cover form a preassembled unit, into which then only the igniter has to be inserted from the inside.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows a longitudinal section through an embodiment of the gas generator according to the invention and  
         [0010]    [0010]FIG. 2 shows a longitudinal section through a second embodiment of the gas generator according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    In FIG. 1 a gas generator is illustrated, the outer housing of which consists of two parts, namely of a cup-shaped receiving part  10  and of a cover  12  closing the receiving part  10 . The receiving part  10  and the cover  12  are of the same plastic and form a gas-tight housing which is protected from the entry of moisture. Through an ultrasonic welding, which is symbolized by the weld seam  14 , the receiving part  10  and the cover  12  are connected with each other. A pyrotechnic propellant charge  16  and an electric igniter  18  are housed in the receiving part  10 . The igniter  18  has an outer housing of several parts which consists of an upper part  19  and a base  20  and which is preferably completely closed to the exterior, whereby the igniter forms a preassembled unit in which a further pyrotechnic propellant charge (not shown) is contained. The base  20  is of plastic, the plastic being the same plastic as that for the receiving part  10  and the cover  12 .  
         [0012]    The base  20  has a radially surrounding projection  22 , which lies in a radial gap  24  between a radially inward projection  26  of the receiving part  10  and a shoulder  28  in the cover  12 . The shoulder  28  is one of the surfaces which defines an opening in the cover  12 , which continues outwards into two small openings  30  in which contact sleeves  32  of brass are inserted.  
         [0013]    The projection  22  of the base  20  is gripped axially as far as possible in the radial gap  24  between the receiving part  10  and the cover  12 . The actual fastening of the igniter  18  to the cover  12  takes place by a welding between the base  20  and the cover  12 , which is symbolized by a surrounding, closed weld seam  36 .  
         [0014]    On the rear face of the base  20 , contact pins  40  protrude from the base, which are inserted into the contact sleeves  32 . The outer ends of the contact sleeves  32  receive connecting lines in the form of connecting cables  42 , the outer ends of the contact sleeves  32  being pressed together in order to thereby fix the connecting cables  42 .  
         [0015]    The production of the gas generator, which is preferably an extremely small gas generator to drive a belt tensioner, takes place as follows: Firstly the contact sleeves are equipped at their outer ends with the connecting cables  42  and are pressed together. Then they are placed into a mould, in which the cover  12  is injection-molded or cast, so that the contact sleeves  32  are embedded into the cover  12 . The openings  30  are thereby gastight and are sealed from the entry of moisture, without additional sealing elements being necessary.  
         [0016]    Then the igniter  18 , in relation to FIG. 1, is inserted from above into the contact sleeves  32  so that the contact pins  40  project into the associated contact sleeves  32 . Now the base of the igniter  18  is ultrasonically welded to the cover  12 , so that an additional sealing of the openings  30  by the base is produced, because the weld seam  36  is surrounding, gastight and is a barrier to the entry of moisture.  
         [0017]    Parallel to this, the propellant charge  16  is filled into the receiving part  10 , a space being recessed for the igniter  18  which is later projecting into the propellant charge  16 .  
         [0018]    Finally, the receiving part  10  and the cover  12  with the igniter  18  are inserted one into another and are welded ultrasonically along the weld seam  14 , this weld seam  14  also being constructed so as to be closed all round and being gastight and protecting against the entry of moisture.  
         [0019]    The electric igniter  18  can have a housing entirely of plastic or only a section of plastic, such as for example the base or, if the housing largely consists of sheet metal sections connected with each other, of a plastic ring which connects sheet metal parts with each other and seals them.  
         [0020]    The gas generator which is shown is distinguished by small dimensions and also a simple manufacture, which can be carried out in few manufacturing steps, whilst maintaining a manufacturing process (ultrasonic welding). The propellant charge does not have a filter chamber, to save additional construction space.  
         [0021]    In the embodiment illustrated in FIG. 1, the igniter housing is self-contained and forms a unit prefabricated separately from the outer housing.  
         [0022]    In the embodiment according to FIG. 2, the parts already mentioned in connection with FIG. 1, which have remained functionally the same, are given the reference numbers which have already been introduced.  
         [0023]    The embodiment shown in FIG. 2 differs from this first embodiment in that before fastening to the outer housing, the igniter does not have an igniter housing which is self-contained and hence also does not form a separately prefabricated unit. Rather, the igniter housing consists of a cap  119  of plastic which is welded onto the cover  12 . Reference number  36  again designates the surrounding weld seam. An igniter charge is filled into the cap  119  before placing onto the cover  12 . Contact pins  40  inserted and potted in the cover  12  project into the space  121  delimited by the cap  119 . On the rear face, the contact pins  40  project into an opening  123  in the cover  12 , into which in addition a holding ring with short-circuiting spring (not shown) in inserted and then a plug for connection to a triggering control is introduced.