Abstract:
A gas generator comprises a housing and a propellant contained in the housing, the propellant, after activation, releases a fluid which is under pressure, and the housing has a first and a second housing part, which are movable relative to each other under pressure and form an overflow opening with a variable flow area depending on the pressure in the housing. Either the first or the second housing part, or both, have spacing means, the spacing means are designed so that in the case of the relative movement of the housing parts with respect to each other, a minimum value of the variable flow area is maintained.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a gas generator comprising a housing and propellant contained in the housing, the propellant releasing, after activation, a fluid which is under pressure, and the housing having a first and a second housing part, which are movable relative to each other under pressure and form an overflow opening or fluid passage having a variable flow area depending on the pressure in the housing.  
         BACKGROUND ART  
         [0002]    Gas generators of the afore-mentioned type are known, for example, from U.S. Pat. No. 5,951,040. These gas generators are used in vehicle occupant restraint systems, in order for example to inflate airbags or to activate belt tensioners. If a sensor establishes that unusual acceleration values are present or if it detects an accident, then the ignition of a charge takes place, whereby a fluid is released which is under pressure. The housing of the gas generator is deformable as a function of the pressure of the released fluid, the housing parts moving with respect to each other as a function of the pressure of the fluid, and freeing an overflow opening. In so doing, substantially the entire fluid flow flows through the fluid passage formed by the overflow opening. The flow area of the overflow opening increases with a rising pressure of the fluid in the housing.  
         SUMMARY OF THE INVENTION  
         [0003]    The invention is based on the problem of optimizing the outflow behaviour of such a gas generator and in particular of preventing a blocking of the fluid flow. This is achieved in a gas generator of the above type in that the first and/or the second housing part have spacing means, the spacing means being designed so that in the case of the relative movement of the housing parts with respect to each other, a minimum value of the variable flow area is maintained. In other words, this means that the two housing parts which in the state of rest of the gas generator lie against each other in a gas-tight manner, are deformed after the activation of the gas generator so that the overflow opening is freed. The spacing means guarantee an outflow of the fluid from the gas generator, because they prevent the overflow opening from being closed again and the fluid flow from being blocked as a result of a continuing deformation of the housing parts. Thereby, at the same time a mechanically weaker construction of the housing is possible, because after activation of the gas generator, a sufficiently large flow cross-section of the overflow opening for an emergence of the generated fluid is maintained, even when the housing parts are pressed against each other by the high pressure in the gas generator.  
           [0004]    If the first and the second housing part is constructed substantially so as to be radially symmetrical, this is particularly favourable, because then the pressure of the released fluid can act uniformly on the housing parts and thereby an excess stressing of individual housing sections is avoided.  
           [0005]    Preferably, the first and the second housing parts form a substantially ring-shaped over-flow opening, because in this case a uniform outflow of the released fluid from the gas generator into the vehicle occupant restaint system is made possible.  
           [0006]    It is also particularly favourable when the first and the second housing parts form a common first contact region before the activation of the propellant, the common first contact region being additionally secured with an adhesive connection. The adhesive connection guarantees an even higher gas-tightness of the gas generator housing in the state of rest. Thereby, the penetration of humidity or other substances having an unfavourable effect on the function of the gas generator is avoided.  
           [0007]    In a preferred embodiment, the spacing means are constructed as corrugations or beads. These can be worked in a particularly simple manner into the housing parts and, moreover, ensure a further reinforcement of the component. The generated fluid can then emerge from the housing through sections of the overflow opening formed in the region between the corrugations or beads. Here, the first housing part can be a cover which closes off the second housing part, for example a combustion chamber wall. The corrugations or beads are then preferably arranged in a region of the cover which is adjacent to the first contact region between cover and second housing part.  
           [0008]    Additionally preferred is an embodiment in which the spacing means are constructed as grooves or as ribs lying adjacent to the first and/or second housing part. The grooves can be produced in a simple and favourably-priced manner by milling on one of the housing parts; the ribs can be connected very easily with one of the housing parts, e.g. by welding, or formed in another manner.  
           [0009]    The invention further comprises a gas generator of the type initially mentioned in that between the first and the second housing part, spacing means are provided, the spacing means being separate from the first and second housing part and designed so that in the case of the relative movement of the housing parts with respect to each other, a minimum value of the variable flow cross-section or flow area is maintained. This means that the two housing parts which lie adjacent to each other in a gas-tight manner in the state of rest of the gas generator, are deformed after the activation of the gas generator so that the overflow opening or fluid passage is freed. The spacing means guarantee an outflow of the fluid out from the gas generator, because they prevent the overflow opening being closed again and the fluid stream being blocked as a result of a further deformation of the housing parts. Therefore, at the same time, a mechanically weaker construction of the housing is possible, because after activation of the gas generator, a sufficiently large flow cross-section of the overflow opening is maintained for an emergence of the generated fluid, even if the housing parts are pressed against each other by the high pressure in the gas generator.  
           [0010]    If the first and second housing part are constructed substantially radially symmetrically, then this is particular favourable, because then the pressure of the released fluid can act uniformly on the housing parts and therefore an over-stressing of individual housing sections is avoided.  
           [0011]    Preferably, the first and second housing part and also the spacing means form a substantially ring-shaped overflow opening, because in this case a uniform outflow of the released fluid is made possible out from the gas generator into the vehicle occupant restraint system.  
           [0012]    It is also particularly favourable if the first and the second housing part form a common first contact region before the activation of the propellant, the common first contact region being additionally secured with an adhesive connection. The adhesive connection guarantees an even higher gas-tightness of the gas generator housing in the state of rest. Therefore, the penetration of moisture or other substances having an unfavourable effect on the function of the gas generator is avoided.  
           [0013]    In preferred embodiments, the spacing means have an L-shaped or half-ring-shaped cross-sectional profile. Spacing means of this shape can be produced in a particularly simple manner and ensure, moreover, a further reinforcement of the component. The generated fluid can then emerge out from the housing through several opening sections, separated from each other, of the overflow opening. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Further features and advantages of the invention will be apparent from the following description of preferred embodiments with reference to the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 shows a gas generator according to the invention;  
         [0016]    [0016]FIG. 2 shows a sectional view of a housing of a gas generator according to the prior art;  
         [0017]    [0017]FIG. 3 shows in a first embodiment of the invention a sectional view of the housing of the gas generator of FIG. 1 with activated gas generator;  
         [0018]    [0018]FIG. 4 shows a top view onto the gas generator of the first embodiment;  
         [0019]    [0019]FIG. 5 shows a perspective view of the housing of the gas generator of the first embodiment;  
         [0020]    [0020]FIG. 6 shows a perspective view of a second embodiment of the housing of the gas generator;  
         [0021]    [0021]FIG. 7 shows a sectional view of the second embodiment of the housing of the gas generator;  
         [0022]    [0022]FIG. 8 shows a perspective view of a third embodiment of the housing of the gas generator;  
         [0023]    [0023]FIG. 9 shows a sectional view of the third embodiment of the housing of the gas generator;  
         [0024]    [0024]FIG. 10 shows a sectional view of a fourth embodiment of a gas generator according to the invention;  
         [0025]    [0025]FIG. 11 shows a sectional view of a fifth embodiment of a gas generator according to the invention;  
         [0026]    [0026]FIG. 12 shows a sectional view of a sixth embodiment of a gas generator according to the invention; and  
         [0027]    [0027]FIG. 13 shows a top view of the spacing means of a gas generator according to the invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0028]    In the figures, a gas generator  10  is shown, which corresponds in structure and function substantially to the gas generator described in the U.S. Pat. No. 5,951,040, incorporated herewith by reference. In the following description parts performing the same function are referred to with the same reference numerals.  
         [0029]    [0029]FIG. 1 shows a gas generator  10  with a central igniter chamber  12 , in which here two igniters  14  are arranged. Alternatively, the igniter chamber  12  can also have only one igniter. The igniter chamber  12  is surrounded by an inner wall  15 , in which channels  16  are situated, only one of which is illustrated here. The channels  16  provide a connection between the igniter chamber  12  and an outer combustion chamber  18 . The igniter chamber  12  and the outer chamber  18  each contain a propellant (not illustrated). The inner wall  15  is connected with an igniter flange  19 , in which the igniters  14  are fastened. The igniters  14  and the chambers  12 ,  18  are surrounded by a multiple-part housing  20 . The housing  20  is constructed substantially from three housing parts  22 ,  24 ,  26 .  
         [0030]    The first bell-shaped housing part  22  comprises a cover section  28 , a wall section  30  delimiting the generator peripherally with gas outlet openings  32 , and a flange section  34 , which can serve for fastening the gas generator to a generator supporting part (not illustrated). In the transition region between the cover section  28  and wall section  30  of the first housing part  22 , beads or corrugations  44  are formed as spacer elements, which extend into the interior of the housing. In a variant (not illustrated), the corrugations  44  can be also be constructed towards the exterior.  
         [0031]    The second housing part  24  is substantially a cylinder ring which delimits the combustion chamber  18  peripherally. At its end facing the first housing part, the second housing part  24  forms an end section  36 , which lies in a first contact region  38  tightly against the cover section  28 . The connection between the end section  36  and the cover section  28  is further secured by an adhesive connection. Between the wall section of the first housing part  22  and the second housing part  24 , an outflow region  39  is situated, through which a fluid connection is produced from the chambers  12 ,  18  to the gas outlet openings  32 .  
         [0032]    The third housing part  26  likewise has a cylindrical wall section  40  and a radially extending base section  42 . The wall section  40  of the third housing part is arranged between the wall section  30  of the first housing part and the second housing part  24  and firmly bonded to the wall section  30 . The base section  42  forms a part of the underside of the gas generator  10  and holds the igniter flange  19  with the igniters  14 .  
         [0033]    In FIG. 2 the housing  20  of a gas generator is illustrated according to the prior art, with the housing parts  22 ,  24 ,  26  enlarged, in two different positions (Position I=dashed line, Position II=continuous line), the significance of which is explained further below.  
         [0034]    [0034]FIG. 3 shows an enlarged cutout of the housing  20  with the three housing parts  22 ,  24 ,  26  according to the invention. The position of the end section  36  of the second housing part  24  corresponds here to that of position II in FIG. 2. The end section  36 , however, only lies partially, with the formation of second contact regions  38 ′, against the corrugations or beads  44  on the cover section  28 . Between the second contact regions  38 ′, an overflow opening  46  is constructed with opening sections  46   a , through which the outer chamber  18  and the outflow region  39  are in fluid connection with each other, as symbolized by the arrow A.  
         [0035]    In the embodiment (not illustrated) having the outwardly constructed corrugations  44 , a contact between the end section  36  and the cover section  28  only exists in the second contact regions  38 ′. The overflow opening  46  with the opening sections  46   a , through which the outer chamber  18  and the outflow region  39  are in fluid connection with each other, is constructed between the second contact regions  38 ′.  
         [0036]    The construction of the corrugations or beads is shown in detail in FIGS. 4 and 5. In each case one bead  44  (see FIG. 5) is arranged here in the transition region between cover section  28  and wall section  30  of the first housing part  22  between two gas outlet openings  32 , respectively.  
         [0037]    The mode of operation of the first embodiment of the gas generator is to be illustrated hereinbelow.  
         [0038]    In FIG. 2 the initial positions I of the housing parts  22 ,  24 ,  26  of the inactive gas generator are shown in dashed lines. This position is the same both in prior art gas generators and gas generators of the invention. On igniting of one or two of the igniters  14 , the pressure in the igniter chamber  12  increases very sharply and by means of mechanical transmission means (not illustrated), the cover section  28  of the first housing part  22  is raised, the adhesive connection being detached (see FIG. 2, Position II). At the same time, the gas released from combustion of the ignition composition flows via the channels  16  into the outer chamber  18  and activates a combustion of the propellant in the chamber  18 . By the high pressure in the outer chamber  18 , however, the second housing part  24  and in particular the end section  36  can be displaced radially outwards into the transition region between cover section  28  and wall section  30 , particularly when the wall thickness thereof is constructed too small. The position reached after this displacement is marked by II in FIG. 2. In gas generators according to the prior art (FIG. 2), after the activation of the gas generator, a blocking of the overflow opening can therefore occur between the first housing part  22  and the second housing part  24 , and the emergence of gas from the gas generator can be prevented.  
         [0039]    In the gas generator according to the invention, as can be seen in FIG. 3, the end section  36  of the second housing part  24  after activation of the gas generator is likewise displaced into the transition region between cover section  28  and wall section  30 ; through the construction of the corrugations or beads  44 , the end section  36 , however, only lies partially against the cover section  28  and ensures that a minimum value of a flow area is maintained. Thereby it is ensured that released gas can pass over from the outer chamber  18  through the overflow opening  46  in arrow direction A into the outflow region  39 , in order to then be able to leave the gas generator via the gas outlet openings  32  and flow into an airbag or into another vehicle occupant protection device (not illustrated).  
         [0040]    In FIGS. 6 and 7 a second embodiment of the invention is illustrated. The second housing part  24  has grooves  48  here in the region of the end section  36  on an outer wall  47 .  
         [0041]    In the state of rest before the activation of the gas generator, the end section  36  lies in a gas-tight connection against the cover section  28  (cf. Position I in FIG. 2). With regard to the function of the gas generator, up to the displacement of the end section  36  of the second housing part  24  into the transition region between cover section  28  and wall section  30  (Position II in FIG. 2), reference is to be made to the statements regarding the first embodiment. Because of the grooves  48 , the end section  36  in Position  11  lies against the cover section  28  only in the second contact regions  38 ′. Released gas can flow out from the outer chamber  18  through the overflow opening  46  in arrow direction A into the outflow region  39  and then reaches the gas outlet openings  32  of the gas generator.  
         [0042]    In the third embodiment illustrated in FIGS. 8 and 9, short ribs  50 , spaced apart from each other, are constructed on the outer wall  47  of the second housing part  24  in the region of the end section  36 . As an alternative to this, the ribs may also be constructed as insert components to be placed in the transition region between the cover section and wall section of the first housing part.  
         [0043]    Also in this embodiment, the end section  36  in the state of rest before the activation of the gas generator lies in a gas-tight connection against the cover section  28  (see Position I in FIG. 2). With regard to function in the initial phase after the activation of the gas generator, reference is likewise to be made to the description of the first embodiment. In the third embodiment, the end section  36 , after activation of the gas generator, lies with the ribs  50  in the second contact regions  38 ′ against the transition region between cover section  28  and wall section  30 . The open regions between the ribs  50  make it possible for gas for be able to flow from the outer chamber  18  through the overflow opening  46  in arrow direction A via the outflow region  39  reliably to the gas outlet openings  32 .  
         [0044]    In FIGS.  10  to  12  further embodiments of the invention are illustrated.  
         [0045]    FIGS.  10  to  12  essentially show the gas generator  10  of FIG. 1. Additionally, above one of the igniters  14 , a cap  13  is arranged which is displaceable on the inner wall  15 .  
         [0046]    Furthermore, between the first housing part  22  and the second housing part  24  there is situated respectively in the various embodiments a spacing means  52 ,  56 ,  60  which is to be described in further detail below.  
         [0047]    The spacing means of the embodiment of FIG. 10 is a cylindrical ring  52  with a substantially rectangular cross-sectional profile. As can be seen in the view onto the cylindrical ring  52  (FIG. 13), the latter has over its entire periphery on its outer side equidistant recesses or grooves  53  which have substantially a semicircular cross-section. Between two grooves  53  respectively a cross-piece or tooth  54  is formed. The cross-pieces  54  lie against the first housing part  22 .  
         [0048]    The spacing means of the embodiment shown in FIG. 11 is a ring  56  with an L-shaped cross-sectional profile. The ring  56  with L-shaped cross-sectional profile, like the cylindrical ring  52 , is provided on its radially outwardly extending end with grooves  57 , between which respectively cross-pieces or teeth  58  are situated, which are in contact with the first housing part  22 . The ring  56  with L-shaped cross-sectional profile lies at its axially extending lower end on the wall section  40  of the third housing part  26 , whereby an as a whole particularly stable bearing of the ring  56  with L-shaped cross-sectional profile is achieved on the housing parts  22 ,  24 ,  26  of the gas generator  10 .  
         [0049]    The spacing means can be further constructed as forms or ring  60  with semicircular cross-sectional profile and grooves  61  with cross-pieces or bridges  62  lying therebetween (FIG. 12). The cross-pieces  62  lie against the first housing part  22 .  
         [0050]    In the following, the mode of operation of the fourth, fifth and sixth embodiment of the gas generator is to be illustrated:  
         [0051]    In the gas generator according to the fourth to sixth embodiment of the invention, the end section  36  of the second housing part  24 , after activation of the gas generator, is likewise displaced into the transition region between cover section  28  and wall section  30 . Through the construction of the grooves  53 ,  57 ,  61  and cross-pieces  54 ,  58 ,  62 , the spacing means  52 ,  56 ,  60 , however, only lies Through the grooves  53 ,  57 ,  61  an overflow opening or fluid passage with several opening sections is formed, and it is thus ensured that a minimum value of a flow area is maintained. Thereby, it is ensured that released gas can pass from the outer chamber  18  through the grooves  53 ,  57 ,  61  into the outflow region  39 , in order to then be able to leave the gas generator via the gas outlet openings  32  and flow into an airbag or into another vehicle occupant protection device (not illustrated).