Abstract:
An inflator ( 10 ), especially for a vehicle occupant restraint system, comprising a combustion chamber ( 24 ) in which solid propellant ( 28 ) adapted to be burnt off while forming a gas is accommodated, a storage chamber ( 26 ) containing a pressure gas ( 30 ), an igniter ( 14 ) and a component ( 20 ) arranged between the combustion chamber ( 24 ) and the storage chamber ( 26 ). There is at least one flow communication between the storage chamber ( 26 ) and the combustion chamber ( 24 ). The component ( 20 ) includes an additional weakened zone ( 22 ) adapted to be destroyed upon activation of the inflator ( 10 ) so as to permit flow of gas from the combustion chamber ( 24 ) into the storage chamber ( 26 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an inflator, especially to a vehicle occupant restraint system in accordance with the preamble of claim  1 . 
       BACKGROUND OF THE INVENTION 
       [0002]    Inflators are supplying, for instance, gas for inflating an airbag or for driving a belt tensioner. It is important in all cases that the generated gas is quickly made available. According to a known technology, the propellant is generated at least partially from a pressurized gas stored in the housing of the inflator. The housing is opened by a pyrotechnic igniter destroying a membrane enclosing the housing to the outside so that the gas can flow out. 
       SUMMARY OF THE INVENTION 
       [0003]    In particular an inflator of the type mentioned in the beginning is known, for example, from the patent specification EP 0 874 744 B1. In the inflator described in the same a combustion chamber filled with solid propellant is arranged within a storage chamber filled with pressure gas. 
         [0004]    It is an object of the invention to improve such inflator. 
         [0005]    In particular such inflator is provided with a combustion chamber in which solid propellant adapted to be burnt off while forming gas is accommodated, a storage chamber filled with pressure gas, an igniter and a component disposed between the combustion chamber and the storage chamber. There is at least one flow communication between the storage chamber and the combustion chamber. The component has an additional weakened zone adapted to be destroyed upon activation of the inflator so as to permit a flow of gas from the combustion chamber to the storage chamber. 
         [0006]    It is an advantage of the inflator that by bursting of the weakened zone an enlarged discharge orifice (larger than the flow communication) can be produced so that gas generated by combusting the solid propellant can flow more quickly into the storage chamber and through the same out of the inflator. It is especially advantageous that with this arrangement a shock wave can be generated by which the outlet membrane of the storage chamber can be opened more quickly than in the case of known inflators. 
         [0007]    Preferably, the storage chamber is closed by a membrane against the environment of the inflator. Such membrane can be connected, preferably welded, in a pressure-tight manner to a housing component of the inflator, especially the storage chamber itself. 
         [0008]    The component can be a cap, for instance, inserted, especially press-fitted, in a housing the inflator. It is possible to insert the component only into the housing or else to press-fit the same into the housing. In both cases the effort is reduced vis-à-vis a component that has to be welded stably in the housing in a pressure-tight manner and for years against a great pressure difference. 
         [0009]    Preferably, the component includes at least one overflow orifice and/or an overflow orifice is formed by at least one passage formed in a circumferential wall of the component and/or an overflow orifice is formed by at least one passage formed in a wall of the housing ( 12 ). So pressure compensation between the storage chamber and the combustion chamber can be reached. Advantageously, the overflow orifice is permanently opened at least prior to activation. The passage is preferably arranged outside the weakened zone and extends in axial direction, i.e. in parallel to the longitudinal axis of the housing. In a preferred manner, plural, for example three, passages equally spaced along the periphery of the component. 
         [0010]    It is of advantage when the sum of all flow cross-sections of the at least one overflow orifice is less at least by the factor 5, preferably by the factor 10, than the flow cross-section of the flow orifice formed by the destroyed weakened zone. It has shown that with such constellation upon igniting the inflator the pressure loss through the overflow orifices is insignificant to safe opening of the both the weakened zone and the membrane toward the environment of the inflator. 
         [0011]    While the combustion chamber is opened vis-à-vis the storage chamber, at least through the overflow orifices in the component, the igniter is closed in a preferably gas-tight and/or pressure-tight manner vis-à-vis the combustion chamber, preferably by an igniting membrane. 
         [0012]    The weakened zone is preferably formed by embossing or milling and/or notches and/or laser abrasions. All these are techniques by which an opening force easy to reproduce and thus the bursting pressure can be precisely adjusted in a simple manner, for example by way of the number and the depth of the different areas of the weakened zone. 
         [0013]    In a preferred manner, the housing forms a pressure chamber which is divided into the combustion chamber and the storage chamber by means of the component. Apart from the overflow orifices in the component, preferably no flow communication is provided between the storage chamber and the combustion chamber. 
         [0014]    The embossings are preferably formed so as to be less deep than the material thickness of the component and do not break the latter. 
         [0015]    The weakened zone of the component and the membrane may be arranged on a longitudinal axis A of the inflator and/or opposite to each other and/or on two opposed sides of the storage chamber. 
         [0016]    By means of the igniter a shock wave can be generated by which the membrane can be destroyed. The afore-mentioned position of the weakened zone and the membrane with respect to each other can especially have a positive effect on the efficiency of the shock wave and thus the destruction of the membrane. Also in the case of the inflator presented here the destruction of the weakened zone of the component advantageously generates a shockwave which extends at least in portions through the storage chamber and destroys the membrane as it is known from the state of the art. It has turned out that generating a shock wave and safely opening the membrane toward the environment of the inflator is performed without problem also in the case of a combustion chamber filled with pressure gas, especially even when there is a flow communication between the storage chamber and the combustion chamber. 
         [0017]    The storage chamber is filled, for instance, with argon, helium or a gas mixture under pressure of up to 500 Bars. It is advantageous that the component closing the storage chamber against the combustion chamber neither has to withstand great forces nor has to be manufactured and inserted in the housing with great effort, as there is at least one flow communication to the combustion chamber in which equally the gas mixture is provided (in the cavities between the solid propellant tablets) at the same pressure. 
         [0018]    In addition, it is possible to arrange a screen in the combustion chamber, preferably in line with the weakened zone of the component and the membrane. It is possible in this way to withhold potential burn-off particles that might be formed by burning off the solid propellant. 
         [0019]    In particular, the housing can have an annularly circumferential indentation on which the component is supported. 
         [0020]    It is further advantageous that the igniter, the igniting membrane and the membrane and/or the screen and the weakened zone of the component are located on the longitudinal axis A of the inflator. In this way optimum ignition of the solid propellant and/or of the pressure gas as well as an efficient formation and propagation of the shock wave and thus destruction of the membrane is achieved. This serves ultimately for a safe and quick functioning of the inflator. 
         [0021]    The inflator can be part of a module comprising an airbag inflatable by the inflator and a fastening means for mounting the module, especially in the interior of the vehicle, wherein the inflator is designed in accordance with at least one of the afore-described configurations. 
         [0022]    Further advantages and features of the invention are resulting from the following description of plural variants with respect to the enclosed drawing, in which 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a schematic cross-section across an inflator according to the invention, with only one half of the inflator being illustrated; 
           [0024]      FIGS. 2 to 4  show views of a component for an inflator according to the invention in a first variant; 
           [0025]      FIGS. 5 and 6  show views of a component for an inflator according to the invention in a second variant; and 
           [0026]      FIGS. 7 and 8  show views of a component for an inflator according to the invention in a third variant. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]      FIG. 1  illustrates an inflator  10  including an elongate cylindrical housing  12  at the first axial end of which an igniter  14  is provided and at the second axial end of which the housing  12  is closed by a membrane  16  against the environment of the inflator  10 . The housing  12  forms the outer housing of the inflator  10 . A diffuser  18  provided with discharge orifices in a known manner is connected to the housing  12  in axial direction and guides the gas flowing out to its location, for instance to an inflatable airbag that is not shown. 
         [0028]    A component  20 , here in the form of a cap pressed into the housing  12  and having an embossed weakened zone  22 , divides the housing  12  in the direction of the longitudinal axis A of the inflator into a combustion chamber  24  and a storage chamber  26 . In the direction of the longitudinal direction A of the inflator the combustion chamber  24  in which a predetermined amount of solid propellant  28 , here in tablet form, is accommodated is formed in the housing  12  adjacent to the igniter  14 . 
         [0029]    The storage chamber  26  separated from the combustion chamber  24  by the component  20  is filled with compressed gas  30  (for instance argon, helium or a suited gas mixture). The component  20  does not close the storage chamber  26  against the combustion chamber  24  in a pressure-tight manner so that a flow communication is provided between the two chambers. Because of this, during manufacture of the inflator  10 , when filling the storage chamber  26  with compressed gas  30  the gas flows through overflow orifices  32  in the component  20  (see for example  FIG. 2 ) also into the combustion chamber  24  until a pressure compensation is reached between the two chambers  24 ,  26 . Prior to activating the inflator  10 , compressed gas  30  is provided both in the storage chamber  26  and in the combustion chamber  24  in mutual flow communication. 
         [0030]    In the variant shown here the component  20  is pressed into the housing  12 , however it could also be simply inserted in the housing  12  or fastened in any other way. 
         [0031]    In the area where the component  20  is mounted in the housing  12  an annularly circumferential indentation  34  on which the component  20  is supported and which additionally secures the component  20  is provided in the housing  12 . 
         [0032]    In order to withhold potential burn-off particles a screen  36  may be inserted ahead of the component  20  in the combustion chamber  24 . 
         [0033]    The igniter  14  is separated from the combustion chamber  24  in a pressure-tight and gas-tight manner. For this purpose, an igniter carrier  38  in which the igniter  14  is accommodated is closed by an igniter membrane  40 . The igniter membrane  40  can be, for instance, a sheet plate made of stainless steel or carbon steel or a similar part that is easy to manufacture. 
         [0034]    Upon activation of the inflator  10  in a known manner the igniter  14  receives an electric signal to ignite the same. The related sudden increase in pressure in the igniter  14  initially destroys the igniter membrane  40  and ignites the solid propellant  28  in the combustion chamber  24 . Due to the sudden increase in pressure in the combustion chamber  24  the weakened zone  22  in the component  20  (cf.  FIG. 2 , for example) is destroyed so that abruptly a large opening related to the diameter of the housing  12  is formed in the component  20 . This abrupt opening generates a shock wave entering the storage chamber  26  and passing the same up to the membrane  16 . The pressure gas  30  in the storage chamber  26  need not heat significantly. In the area of a local shock wave front there is an extremely short-term increase in pressure which frequently exceeds the bursting pressure of the membrane  16  and opens the latter only in the area of the shock wave. In this way, very early opening after activation of the inflator  10  is effectuated. The temperature in the combustion chamber can be, for instance, within the range of 2900 K, wherein the pressure in the combustion chamber  24  can increase to values ranging from 875 to 1125 Bar. The velocity of the shock wave can be between 750 and 1250 m/sec. 
         [0035]    The inflator illustrated here can be used, for example, for inflating an airbag, especially a passenger airbag, but also for other purposes. 
         [0036]    The component  20  can have a quite variable design. It is merely necessary that prior to activating the inflator  10  a pressure compensation can take place between the storage chamber  26  and the combustion chamber  24  and the weakened zone  22  is reliably destroyed upon activation of the inflator  10 . 
         [0037]    A first variant of the component  20  is shown in detail in the  FIGS. 2 to 4 . The component  20  substantially exhibits the form of a cap having an approximately hemi-spherical cover  42  including an adjacent frusto-conical circumferential wall  44 . In the crest of the cover  42  a star-shaped embossing is provided that forms the weakened zone  22 . The bursting pressure of the weakened zone  22  can be adjusted by way of the number, the length and the depth of the embossings in a very accurate and well reproducible fashion. Apart from the shown star-shaped embossing, the weakened zone  22  can also have a cross-shaped, C-shaped or ring-shaped embossing. 
         [0038]    In the circumferential wall  44  three axially extending passages evenly spaced along the periphery are designed as overflow orifices  32 . When the component  20  is inserted in the housing  12 , the overflow orifices  32  form a flow communication between the storage chamber  26  and the combustion chamber  24 , because the circumferential wall  44  of the component  20  is not completely adjacent to the inner wall of the housing  12  but is spaced apart therefrom in the area of the overflow orifices  32 . 
         [0039]    It is possible to press-fit the component  20  or else to merely insert the same in the housing  12  without press-fitting. 
         [0040]    Upon activation of the inflator  10  the embossing ruptures in the weakened zone  22  so that a relatively large opening occurs which preferably extends beyond more than half of the entire diameter of the housing  12 . The amount of gas which upon activation of the inflator  10  flows through the overflow orifices  32  bypassing the component  20  from the combustion chamber  24  into the storage chamber  26  is negligible and smaller by at least the factor 10 than the amount of gas flowing through the ruptured weakened zone  22 . Thus the overflow orifices  32  have no influence on the generation of the shock wave by destruction of the weakened zone  22 . 
         [0041]    The component  20 , and especially the circumferential wall  44  thereof, can also be configured such that, when the pressure is increased in the combustion chamber  24 , in this area and in the area of the overflow orifices  32  the component  20  is adjacent to the inner wall of the housing  12  so that the overflow orifices  32  are closed completely or partly by deformation of the circumferential wall  44 . 
         [0042]    The  FIGS. 5 and 6  illustrate a component  20 ′ in a second variant. The frusto-conical circumferential wall  44  including the overflow orifices  32  is configured identically to the afore-described embodiment. The cover  42 ′ has a flatter curvature than in the afore-described component  20 , however. The embossing in the weakened zone  22  is star-shaped in this case, too. 
         [0043]    The  FIGS. 7 and 8  illustrate a third variant of the component  20 . In this case the component  20 ″ merely consists of the cover  42 ″. In the marginal area the cover  42 ″ is curved in a slightly convex manner so as to permit better fitting into the housing  12 . It is also imaginable that the cover  42 ″ has no curvature and thus has a substantially planar shape. Here, too, the weakened zone  22  is configured by a star-shaped embossing. In this case no specifically formed overflow orifices are provided and the pressure compensation between the storage chamber  26  and the combustion chamber  24  is performed preferably by the fact that the component  20 ″ is not inserted in the housing  12  in a pressure-tight manner. 
         [0044]    The inflator may also be mounted in a module comprising an airbag inflatable by the inflator and a fastening means for mounting the module, especially in the interior of a vehicle, the inflator being designed according to at least one of the afore-described configurations. The module, the airbag and the fastening means for mounting the module are not illustrated in the figures.