Abstract:
A gas generator includes a housing having an inner wall delimiting an igniter chamber peripherally, and at least one igniter opening into the igniter chamber. The gas generator further includes a cap arranged for displacement along the inner wall and delimiting the igniter chambe, said cap having a cylindrical peripheral wall and a radially extending cover wall. The peripheral wall has a first section extending from the cover wall in displacement direction (R) and a second section extending in a direction opposite thereto. The first and second sections lie against the inner wall and guide the cap during a displacement thereof. The cover wall is turned axially into the interior of the cap.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a gas generator.  
         BACKGROUND OF THE INVENTION  
         [0002]    Known gas generators have a housing with an inner wall delimiting an igniter chamber peripherally, at least one igniter opening into the igniter chamber, and a cap arranged for displacement along the inner wall and delimiting the igniter chamber, which cap has a cylindrical peripheral wall and a radially extending cover wall. The cap is preferably constructed such that it covers the outflow opening before the activation of the gas generator and during the activation of the gas generator and the displacement of the cap, it exposes the outflow opening.  
           [0003]    Such a gas generator is described, for example, in U.S. Pat. No. 6,315,322 B1.  
           [0004]    The invention meets the problem of optimizing the behavior of such a gas generator shortly after its activation.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    According to the invention, a gas generator includes a housing having an inner wall delimiting an igniter chamber peripherally, and at least one igniter opening into the igniter chamber. The gas generator further includes a cap arranged for displacement along the inner wall and delimiting the igniter chamber, said cap having a cylindrical peripheral wall and a radially extending cover wall. The peripheral wall has a first section extending from the cover wall in displacement direction and a second section extending in a direction opposite thereto. The first and second sections lie against the inner wall and guide the cap during a displacement thereof. Together with the cover wall, the second section of the peripheral wall defines a precisely defined igniter chamber volume at the start of ignition of the gas generator. Owing to the long guidance of the cap, the displacement movement of the cap is able to be predetermined more precisely. After the displacement of the cap, it is also ensured by the first section and the cap shape as a whole that the volume available for the combustion of the propellant in the igniter chamber, and the increase in volume, is precisely defined. All these points contribute to making the ignition behavior of the gas generator precisely reproducible and able to be determined in a defined manner. When the cap initially closes an outflow opening in the inner wall, the moment of opening the outflow opening is likewise clearly defined by the cap shape.  
           [0006]    These advantages are also achieved by a gas generator according to claim  14 .  
           [0007]    In the igniter chamber, preferably a propellant charge is contained, which can serve as a booster charge.  
           [0008]    The sections of the peripheral wall are cylindrical in the embodiments shown here and have identical external diameters, so that the cap can be simply inserted into the preferably likewise cylindrical igniter chamber.  
           [0009]    It has been found that a good guidance of the cap in the igniter chamber is to be achieved when the axial length of the first section corresponds approximately to the axial length of the second section.  
           [0010]    In order to seal with respect to the exterior the volume surrounded by the second section and the cover wall, and the charge contained therein, and also in order to obtain a defined displacement resistance, at least the first section lies against the inner wall under prestress. The second section can also be prestressed accordingly.  
           [0011]    A defined end of the displacement process and hence a defined maximum volume of the igniter chamber can be established by provision being made that the first section strikes against a housing part of the gas generator at the end of the displacement. The striking action can of course likewise take place at component separate from the housing and arranged in the gas generator. Preferably, the first section is constructed to be so rigid that it is not plastically deformed at the end of the displacement, in order to obtain the defined volume proportions.  
           [0012]    In a preferred embodiment, the sections continue into each other in one piece. Also, the peripheral wall and the cover wall are connected with each other in one piece. This can be simply achieved when the cap is a one-piece sheet metal shaped part, the peripheral wall and the cover wall being formed by deformation of the sheet metal shaped part. In this way, a favorably priced production and also a low weight of the cap are the result.  
           [0013]    The first and/or the second section can be at least partially realized so as to be double-walled, which also increases the stability of the cap. The double-walled construction can be achieved simply by a deformation process, for example.  
           [0014]    Preferably, the peripheral wall is turned partially into the interior of the cap by plastic axial drawing of the cover wall, and is constructed so as to be double-walled in the turned-in region. For stability, it is advantageous here if the inner wall section lies against the outer one in the double-walled region of the peripheral wall. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 shows a gas generator according to the invention;  
         [0016]    [0016]FIG. 2 shows a variant of the gas generator of FIG. 1;  
         [0017]    [0017]FIG. 3 shows a further variant of a gas generator;  
         [0018]    [0018]FIG. 4 shows a variant of the gas generator of FIG. 3; and  
         [0019]    [0019]FIG. 5 shows a cap for use in a gas generator according to FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    In the figures, a gas generator  10  is shown, which corresponds in structure and function substantially to that described in U.S. Pat. No. 6,315,322 B1. With respect to the features known from this publication, reference is therefore to be made thereto.  
         [0021]    The housing of the gas generator  10  has an inner wall  14  surrounding peripherally a clearance volume  11  and an igniter chamber  12  lying therebeneath, at the (lower, in the figures) end of which an igniter  16  is arranged such that its upper end opens into the igniter chamber  12 . In the inner wall  14 , outflow openings  18  are provided, only one of which is shown here, by means of which gas generated in the igniter chamber  12  can overflow into a combustion chamber  20 . The combustion chamber  20  is filled with a suitable propellant which is not shown here.  
         [0022]    A cap  22  which is displaceable along the inner wall  14  separates the clearance volume  11  from the igniter chamber  12 . The cap  22  has a circular cylindrical peripheral wall  24  which, viewed in axial direction, has an upper first section  26  and a lower second section  28  adjoining thereto. In the example shown here, the diameters of the first and of the second section  26 ,  28  are identical, and the diameter of the cap  22  and of the igniter chamber  12  are selected such that both the first and the second section  26 ,  28  lie under prestress against the inner wall  14  over the entire periphery.  
         [0023]    The cap  22  is displaceable in axial direction in displacement direction R (see arrow) against a resistance in the igniter chamber  12  which is determined by the prestress.  
         [0024]    The second section  28  is delimited by a radially extending cover wall  30 . In the volume formed by the cover wall  30  and the second section  28 , a charge  32  is accommodated, which can undertake for example the function of a booster charge for the igniter  16 .  
         [0025]    The cap  22  is arranged such that it covers the outflow opening  18  before the ignition, i.e. activation, of the gas generator  10 .  
         [0026]    Before activation of the gas generator  10 , the cap is positioned entirely at the lower end of the igniter chamber  12  (the lower edge of the section  28  abuts against a shoulder) and directly over the free end of the igniter  16 . The volume of the igniter chamber  12  in which the propellant charge  32  is contained, is thereby precisely defined.  
         [0027]    In the embodiment shown, the cap consists of a one-piece deformed sheet metal part, so that both the first section  26  and the second section  28  and also the peripheral wall  24  and the cover wall  30  continue into each other in one piece. The shape of the cap  22 , an “H” in section, is achieved in that the peripheral wall is partially turned into the interior of the cap by plastic axial drawing of the cover wall. This leads to the first section  28  being constructed with double walls, the inner wall section lying against the outer one. It is also conceivable to additionally construct the first section  26  likewise with double walls.  
         [0028]    Instead of being of metal, the cap  22  can also be produced from a suitable plastic or another suitable material; for example, it may also be constructed as a cast part or a punched bent part instead of a deformation part.  
         [0029]    On activation of the gas generator  10 , firstly the igniter  16  and shortly thereafter the propellant charge  32  are ignited. Owing to the gas development, at a moment after ignition determined inter alia by the displacement resistance of the cap  22  in the igniter chamber  12 , the cap  22  is displaced upwards in direction R in the igniter chamber  12 , the outflow opening  18  into the combustion chamber  20  being exposed. Through the hot gases flowing over, the propellant contained in the combustion chamber  20  is then ignited. The volume of the igniter chamber  12  increases in a manner which can be predetermined very precisely, and that of the clearance volume  11  decreases correspondingly.  
         [0030]    The prestress of the peripheral wall  24  against the inner wall  14  is so great that there will also be ensured a sealing against the flowing over of gas into the clearance volume  11  or into the remaining gas generator  10 .  
         [0031]    On burning of the propellant charge situated in the igniter chamber  12 , the peripheral wall  24  is pressed radially against the inner wall  14 , the displacement resistance and the sealing action being increased.  
         [0032]    The displacement of the cap  22  ends when the axial edge  211  (upper edge) of the first section  26 , facing away from the igniter  16 , strikes against a housing part or another component arranged in the housing of the gas generator  10 . The cap  22  is constructed such that the first section  26  has such an inherent rigidity that on striking, no plastic deformation of the cap  22  takes place. Hereby, the igniter chamber volume, which influences the burning behavior of the propellant charge  32 , remains precisely defined. In the example shown here, the axial length of the first section  26  corresponds approximately to the axial length of the second section  28 .  
         [0033]    The variant of the gas generator  10  shown in FIG. 2 differs from that shown in FIG. 1 merely in that the cap  22  is inserted into the igniter chamber  12  rotated through 180 degrees. In this case, therefore, the first section  26  is double-walled and the second section  28  is only one-walled in construction, whereby the stability of the first section  26  is higher than in the example in FIG. 1. Advantages and mode of operation of the gas generator  10  are as set forth above.  
         [0034]    In both embodiments, the pressure increase in the gas generator leads to elastic deflections of housing parts  100  to  140  relative to each other. Through the relative movements of the housing parts  100  to  140  with respect to each other, flow paths become free (see arrows), so that the gas finally arrives out of the gas generator via outflow openings  150 .  
         [0035]    In FIGS.  3  to  5 , further possible forms of cap are illustrated. Only the components relevant to the description are provided with reference numbers. The remaining construction and mode of operation of the gas generators shown is as described above.  
         [0036]    In the variant shown in FIG. 3, the cap  322  has a cylindrical peripheral wall  324  and a cover wall  330  which is turned in in the center in a trough shape. The turning in is rounded off and can, for example, be hemispherical. The cover wall  330  is connected at one end of the cap  322  in one piece with the peripheral wall  324 . The cap  322  is inserted into the gas generator such that the free end of the peripheral wall  324  is directed to the igniter  16 . The igniter chamber  12  is delimited at the top by the cover wall  330  which is convex when viewed from the interior. The volume of the igniter chamber  12  can be defined exactly by the degree of turning in of the cover wall  330  in the direction of the igniter  16 .  
         [0037]    The peripheral wall  324  lies under prestress against the inner wall  14  of the igniter chamber  12 , so that a defined resistance has to be overcome to displace the cap  322 , and the igniter chamber  12  is sealed against the clearance volume  11  situated above the cap  322 .  
         [0038]    Here also, as in FIGS. 4 and 5, on burning of the charge (see FIG. 1) situated in the igniter chamber  12 , the peripheral wall  324  is pressed radially against the inner wall  14 , the displacement resistance and the sealing action being increased.  
         [0039]    The cap  422  shown in FIG. 4 is shaped similarly to the cap  322  shown in FIG. 3. Here, in fact, the cover wall  430  is turned in in the shape of a truncated cone in cross-section, and in addition the cap  422  is inserted into the gas generator turned through 180 degrees with respect to the cap  322  of FIG. 3. Viewed from the direction of the igniter  16 , the cover wall  430  therefore forms a concave boundary to the igniter chamber  12 .  
         [0040]    In FIG. 5 a further variant of a cap  522  is shown. The difference to the cap  422  illustrated in FIG. 4 lies in that the turning in of the cover wall  530  is constructed so as to be rounded off in the center of the cover wall, i.e. without edges. In FIG. 5 by way of example, measurements are indicated for the individual sections of the cap  522 . These measurements can also be transferred to the other described caps  22 ,  322 ,  422 . The diameter D of the cap  522  amounts to 13.3 mm, the height h to 13 mm, 0.6 mm is selected here as wall thickness d, and the radii of curvature of the turning in R e  or at the transition between peripheral wall  524  and cover wall  530  R ë  amount to 1.5 mm and 0.9 mm, respectively.  
         [0041]    Also in the embodiments according to FIGS.  3  to  5 , at the end of the displacement path the upper axial edge  211  of the peripheral wall  324 ,  424 ,  524  strikes against the housing part  110 .  
         [0042]    The cover wall  30  of the embodiments according to FIGS. 1 and 2 can also have a shape corresponding to the cover wall  322 ,  422 ,  522 .