Abstract:
A gas generator has a combustion chamber containing a pyrotechnic propellant charge and a biasing unit biasing the propellant charge. A holding device is provided, which holds the biasing unit in a predetermined, fixed, compressed position and which is designed to be releasable, so as to selectively release the biasing unit, so that it arrives at a release position in which it exerts a biasing force on the propellant charge.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a gas generator.  
       BACKGROUND OF THE INVENTION  
       [0002]     The propellant charge accommodated in a gas generator for vehicle occupant restraint systems is mechanically biased so that during the years of driving operation it cannot move. This is especially important with a tablet-charge filling, because the tablets would rub against each other and would wear away. The biasing units used heretofore have been, by way of example, springs or foam inserts. A pyrotechnic gas generator is usually closed by welding, it being important in the process to prevent the pyrotechnic propellant charge from igniting during the welding as a result of a spark.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0003]     It is an object of the present invention to provide a gas generator which is easy to fill and whose individual parts can be welded to each other in a simple manner.  
         [0004]     To achieve this object, a gas generator comprises a combustion chamber containing a pyrotechnic propellant charge and a biasing unit biasing the propellant charge. A holding device is provided, which holds the biasing unit in a predetermined, fixed, compressed position and which is designed to be releasable, so as to selectively release the biasing unit, so that it arrives at a release position in which it exerts a biasing force on the propellant charge.  
         [0005]     The biasing units customary heretofore, e.g., springs, were usually inserted into the combustion chamber first, and then the propellant charge was pressed into the combustion chamber through the application of external force, so that the spring became compressed. Still other systems provided that the combustion chamber, open on one side, is closed by a cover after the filling of the propellant charge, the biasing unit being positioned on the interior side of the cover.  
         [0006]     In contrast, the present invention provides that the biasing unit, as the gas generator is filled, is kept in a compressed position by the holding device, without its exerting the biasing force on the propellant charge in this context. In this position, the biasing unit is more compressed than in the subsequent release position. Only in the release position the biasing unit exerts the biasing force on the propellant charge and a non-fixed position results, which is determined by an equilibrium of forces between the biasing unit and the opposing pressure of the propellant charge. Due to the fixed, compressed position, the propellant charge can be filled without pressure having to be exerted on the propellant charge during the filling process and during the subsequent closing process of the combustion chamber. In addition, the compressed position makes it possible to not completely fill the combustion chamber with propellant charge before it is closed, so that, when the combustion chamber is closed, specifically by welding, the propellant charge can be at a sufficient distance from this joining location. Thus, there is no danger of igniting the propellant charge when the gas generator or the combustion chamber are closed. Only after the closing can the holding device be released, as a result of which the biasing unit arrives in the release position.  
         [0007]     According to the preferred embodiment, the holding device is a mechanical locking means, which engages, for example, the combustion chamber wall, the exterior housing of the gas generator, or, according to the preferred embodiment, another section of the holding device, so that in the latter case the holding device forms a self-contained unit, which in the compressed position maintains itself in a stable state.  
         [0008]     The biasing unit should be a preassembled unit, which can be inserted into the combustion chamber as such, already in the compressed position, thus making the assembly process easier.  
         [0009]     The biasing unit has, e.g., a front wall facing the propellant charge, a rear wall facing away from the propellant charge, as well as an elastic spring element between them, and is thus designed so as to have very few parts.  
         [0010]     The front wall and the rear wall are alternatively joined to each other by the holding device firmly and at a constant distance in the compressed position, and they are uncoupled from each other in the release position. “Uncoupled” means that the front and rear walls are released from each other such that the front wall can move freely towards the propellant charge.  
         [0011]     The holding device includes, for example, extensions protruding from the front wall, which engage, e.g., the rear wall. Of course, inversely, the rear wall could also carry the extensions, which would engage the front wall.  
         [0012]     In order to grant a simple and rapid release, it is preferably provided that the holding device has a turning lock, in particular a bayonet lock, and that it attains the release position by turning the lock.  
         [0013]     The combustion chamber is delimited on the exterior side by a combustion chamber wall, the biasing unit being located at an axial end of the preferably elongated, cylindrical combustion chamber. The opposite end of the combustion chamber is the filling side for the propellant charge and is the side of the combustion chamber or of the entire generator that is closed, specifically by welding, after the filling process.  
         [0014]     The biasing unit is inserted into the combustion chamber specifically through the filling-side axial end and contacts the combustion chamber laterally in a stable manner, so that the motion of the biasing unit can only take place in one direction.  
         [0015]     The biasing unit is accommodated in the combustion chamber in an unsecured manner, as is provided by one embodiment, i.e., a form-fitting connection between the combustion chamber wall and the biasing unit is not necessary. Rather, the biasing unit is clamped between one axial end of the combustion chamber wall and the propellant charge.  
         [0016]     The present invention is not limited to pure pyrotechnic gas generators. The preferred embodiment even provides an elongated hybrid gas generator, in which the combustion chamber is surrounded by a gas-filled pressure chamber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     In the drawings:  
         [0018]      FIG. 1  depicts a schematic partial sectional view of a gas generator according to the present invention,  
         [0019]      FIG. 2  depicts a somewhat modified embodiment of the combustion chamber insert shown in  FIG. 1 , having an integrated biasing unit, and  
         [0020]      FIG. 3  depicts a top view of the rear wall of the biasing unit used in the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]     In  FIG. 1 , a hybrid gas generator  10  is shown, having an elongated, cylindrical external housing  12 , which surrounds a pressure chamber, which is filled with a medium  13  that is under pressure, e.g., an inert gas such as argon or helium. Exterior housing  12  has an elongated shape and has a circumferential wall  14 , which in the axial direction A tapers to a cone at both ends of gas generator  10 .  
         [0022]     Located at an axial filling end of gas generator  10  is a pot-shaped cover  15  and an ignition unit  16  that is connected to it, the ignition unit being known from conventional hybrid gas generators. In the example depicted here, ignition unit  16  is closed off from the pressure chamber by a diaphragm  17 , which is destroyed when ignition unit  16  is activated. At the opposite axial end of gas generator  10 , discharge openings  22  as well as a choke device  18  and a closure diaphragm  20  are provided. After closure diaphragm  20  is opened, the pressure chamber is in fluid communication with discharge openings  22  through choke device  18 , so that gas can escape from gas generator  10 .  
         [0023]     In the interior of exterior housing  12 , an elongated combustion chamber wall  24  is received like an insert in which combustion chamber  25  is configured, which is filled with a propellant charge  26  in tablet form. Propellant charge  26  is exclusively accommodated in combustion chamber  25 . A first axial end  28  of combustion chamber  25  borders on choke device  18 , whereas a second axial end  29  of combustion chamber  25 , also known as the filling end, is located on the side of ignition unit  16 .  
         [0024]     Combustion chamber wall  24  is manufactured from a perforated plate and radially delimits the combustion chamber to the outside. Combustion chamber wall  24  at first end  28  has large through openings  32 , and at first end  28  terminates in a chamfer  34  which has the shape of a truncated cone. Distributed over its entire circumference, tubular combustion chamber wall  24  has additional smaller openings  40 .  
         [0025]     At second end  29 , a chamfer  45  is also provided, by which combustion chamber wall  24  is supported on circumferential wall  14 , which in this area tapers conically. By chamfers  34 ,  45 , combustion chamber wall  24  is fixed in position in exterior housing  12  both radially and axially.  
         [0026]     In the area of end  28 , there is a biasing unit  50  in combustion chamber  25 , assuring that propellant charge  26  is biased.  
         [0027]     Biasing unit  50  is made up of three parts, as can be discerned more easily in  FIG. 2 , i.e., a front wall  52 , which is depicted in  FIG. 1  in two positions, an annular rear wall  54  that is provided with a large through opening, and a symbolically depicted spring  56 , that is arranged between walls  52 ,  54 , the spring urging both walls  52 ,  54  away from each other axially. Front wall  52  is configured so as to be crown-shaped and on its outer edge has integrally-formed finger-shaped extensions that point toward rear wall  54 . Specifically, four longer extensions  58  are distributed over the circumference, which, in one position (compressed position), engage behind rear wall  54 , as well as, between longer extensions  58 , short extensions  60 , that in contrast to the former are not bent at the free end and that, on the front-side free end, contact rear wall  54 , in the so-called compressed position of biasing unit  50 .  
         [0028]     Biasing unit  50  is a self-contained, preassembled unit, extensions  58 ,  60  constituting a holding device between the two walls  52 ,  54  and being part of a bayonet lock, i.e., generally a turning lock. The bent, longer extensions  58  in fact extend through recesses  62  that are provided in segments on the exterior edge of rear wall  54  (see  FIG. 3 ), the recesses enlarging radially to the inside forming insertion recesses  64 .  
         [0029]     Biasing unit  50  is preassembled in the following way. Spring  56  is inserted into pot-shaped front wall  52 . Then, starting from the rear side, rear wall  54  is placed in position, long extensions  58  being aligned with recesses  64 , so that rear wall  54  can be pressed near to front wall  52  in opposition to the spring force and then can be turned like a bayonet lock, extensions  58  thus finally being situated in the areas of recesses  62 . In this state, biasing unit  50  is a self-contained unit having a compressed spring contained therein, front and rear walls  52 ,  54  being held in position at a fixed distance.  
         [0030]     To make it easier to turn front wall  52  and rear wall  54  in relation to each other, through opening  66  in rear wall  54  is designed so as to be hexagonal. Alternatively, of course, this through opening  66  could be designed so as to be larger and, instead of this, a depression or recess could be configured in front wall  52  for inserting a tool.  
         [0031]     In this compressed position, biasing unit  50  is pushed from axial end  29  into combustion chamber  25 , the outside diameter of walls  52 ,  54 , being proportioned in relation to the inside diameter of combustion chamber wall  24  so as to be virtually without play. Then the inwards-pointing, hook-shaped ends of long extensions  58  contact a shoulder in the area of chamfer  34  (left-hand position of the front wall  52  in  FIG. 1 ). This inserting of biasing unit  50  is accomplished when the gas generator is upright, with end  29  pointing upwards. Subsequently, propellant charge  26  is filled in, combustion chamber  25  being not completely filled. Then the unit made up of cover  15  and ignition unit  16  is placed from above onto the not yet closed opening in the exterior housing. Finally, circumferential wall  14  and cover  15  are welded, with the gas generator still in the upright position. Due to the compressed, compact biasing unit, there is so much additional volume in combustion chamber  25  available for propellant charge  26 , that the latter does not come into contact with cover  15  during the welding process, so that a gap exists between the propellant charge volume and cover  15 .  
         [0032]     After the welding, rear wall  54  is rotated via the left, still open side using a hexagonal tool, so that extensions  58  can leave recesses  64 , and front wall  52  presses axially against the propellant in the direction of the arrow in FIG. I and is uncoupled from rear wall  54 . The right-hand position of front wall  52  indicated in  FIG. 1 , resulting thereby, is the so-called release position, in which biasing unit  50  exerts a biasing force on propellant charge  26 , which in this context moves to the right and is clamped between cover  15  and front wall  52 .  
         [0033]     Subsequently, gas generator  10  is filled with pressurized gas via the left, open front side and finally is closed using the unit that is made up of choke device  18  and closure diaphragm  20 . This closing is preferably likewise accomplished by welding.  
         [0034]     In the embodiment according to  FIG. 2 , only first end  28  is somewhat differently configured. Biasing unit  50  is depicted in the release position, and for purposes of clarity propellant charge  26  is omitted.