Abstract:
The invention relates to a bursting diaphragm ( 14 ) for an inflator ( 10 ) comprising at least one predetermined breaking contour ( 24 ) destroyable upon activation of the inflator ( 10 ), wherein a shock wave can be generated. In accordance with the invention, the predetermined breaking contour ( 24 ) includes a through hole ( 25 ) on at least one end point ( 27 ), especially on all end points ( 27 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a bursting diaphragm, especially for an inflator, comprising at least one predetermined breaking contour destroyable upon activation of the inflator, wherein a shock wave can be generated. Apart from that, the invention relates to an inflator, an airbag module as well as a vehicle safety system. 
     Inflators supply gas for filling an airbag or for driving a belt tensioner, for example. In both cases it is important that the generated gas is quickly available. According to a known technology, this gas is generated at least partly of a pressurized gas stored in the housing of the inflator. A membrane closes the housing in which the pressurized gas is stored in a fluid-tight manner. The housing is opened in that upon activation of the inflator a pyrotechnic igniter destroys the membrane so that the gas can flow out. 
     Such inflator is known, for example, from the laid-open print 2005/0206145 A1. This inflator includes a combustion chamber in which an igniter adapted to be activated while pressure is developed is accommodated. Moreover a supply chamber filled with compressed gas is provided which is closed in a pressure-tight manner in the non-activated state of the inflator against the combustion chamber by a breakable membrane. The breakable membrane includes a weakened zone which is destroyable upon activation of the inflator so as to provide a fluid communication between the combustion chamber and the supply chamber filled with compressed gas upon activation of the inflator. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to further develop such membrane. Moreover it is the object of the invention to describe an inflator, an airbag module as well as a vehicle safety system comprising such membrane. 
     In accordance with the invention, this object is achieved with respect to the further developed bursting diaphragm by the subject matter of claim  1 . 
     The invention is thus based on the idea to describe a bursting diaphragm, especially for an inflator, comprising at least one predetermined breaking contour destroyable upon activation of the inflator, wherein a shock wave can be generated, the predetermined breaking contour having a through hole on at least one end point, especially on all end points. 
     A predetermined breaking contour preferably has at least two end points, the end points describing for example the end areas of linear or curved geometries. The predetermined breaking contour has a through hole on at least one end point, especially on all end points. The advantage of the bursting diaphragm according to the invention consists in the fact that the through hole or through holes in the bursting disk allow to dispense with a pressure-tight design of the bursting disk. This is to say that the bursting disk need not be fastened in a complicated pressure-tight manner to the housing of the inflator, as it constitutes no pressure-tight closing-off for pressurized gas inside the inflator. Moreover, the through hole or through holes in the bursting diaphragm offer the option to store a larger amount of pressurized gas in an inflator, as, apart from a pure pressure storage chamber provided on one side of the bursting diaphragm, on the other (opposite) side of the bursting diaphragm, for instance in a combustion chamber containing pyrotechnic propellant, further space can be used for additional storage of pressurized gas. 
     The predetermined breaking contour is destroyed upon activation of the inflator and the bursting diaphragm ruptures along the predetermined breaking contour, wherein a shock wave is generated, as will be described in more detail further below. In order to allow destruction and generation of a shock wave the predetermined breaking contour is designed to be C-shaped and/or double C-shaped and/or H-shaped and/or T-shaped and/or star-shaped and/or circle segment-shaped and/or cross-shaped. 
     The bursting diaphragm can have an outer contour which is cap-shaped and/or semicircular. The contour of the shell surface of the bursting diaphragm is referred to as outer contour of the bursting diaphragm. In other words, the bursting diaphragm can take the shape of a cap having a semicircular lid including an adjacent frusto-conical or cylindrical circumferential wall. Moreover it is possible that the bursting diaphragm has a frusto-conical or cylindrical circumferential wall, wherein the lid merely has a flat bulge. Also the formation of a flat lid is possible. 
     The through hole of the predetermined breaking contour can be circular. The through hole has at least one opening width, especially having a diameter of from 0.5 to 3.00 mm, especially of from 1.0 to 2.5 mm, especially of from 1.2 to 2.0 mm, especially of 1.4 mm. If the through hole is circular, the opening width can be referred to as diameter. 
     Preferably the shell surface of the bursting diaphragm has a uniform material thickness. In other words, the shell surface of the bursting diaphragm can exhibit the same material thickness continuously and on the entire shell surface, respectively. 
     The predetermined breaking contour of the bursting diaphragm is preferably incorporated in the lid of the shell surface of the bursting diaphragm which can be semicircular and/or bulged and/or flat. The predetermined breaking contour can be formed by stampings and/or millings and/or notches and/or laser abrasions. The predetermined breaking contour forms a weakened zone of the bursting diaphragm so that the shown types of the possible configurations of the predetermined breaking contour are appropriate methods by which an opening force to be appropriately reproduced and thus the bursting pressure can be precisely adjusted, for example via the number and the depth of the different areas of the stampings and/or millings and/or notches and/or laser abrasions. 
     The stampings and/or millings and/or notches and/or laser abrasions preferably have a smaller material thickness than that of the shell surface and do not rupture such shell surface. 
     As regards an inflator, the object is achieved by the features of claim  7 . 
     Such inflator according to the invention has a bursting diaphragm according to the invention. Preferably the inflator comprises at least one combustion chamber filled with fuel and gas and having a discharge end. Furthermore the inflator comprises at least one igniter unit by which the fuel can be ignited. The igniter unit can be provided, for example, in the form of a pyrotechnic igniter. The bursting diaphragm is connected to an external housing of the inflator preferably by material connection and/or form fit. A material connection of the bursting diaphragm to the external housing of the inflator can be made by adhesive bonding and/or welding, for example. A form-fit connection of the bursting diaphragm to the external housing of the inflator is made, for example, by clamping or an appropriate clamping connection. 
     In the inactivated or non-activated state of the inflator, i.e. in a non-ignited state, the bursting diaphragm separates the combustion chamber from a gas supply chamber. The at least one through hole of the predetermined breaking contour is configured as fluid communication or flow communication between the combustion chamber and the gas supply chamber. 
     Summing up, it can be stated that the inflator comprises at least one combustion chamber in which fuel, especially solid fuel, adapted to be burnt while gas is developed is accommodated. Moreover, the inflator comprises a supply chamber filled with gas, especially compressed gas, and an igniter and a bursting diaphragm arranged between the combustion chamber and the supply chamber. There is at least one flow or fluid communication between the supply chamber and the combustion chamber. The bursting diaphragm includes an additional predetermined breaking contour destroyable upon activation of the inflator, wherein a shock wave can be generated. In detail this means that by the combustion of the fuel in the combustion chamber higher pressure is built up than it is prevailing in the supply chamber filled with gas. When the burst pressure of the bursting diaphragm is reached or exceeded, the latter opens and thus ruptures along the predetermined breaking contour so as to permit an abrupt relatively large-surface pressure compensation between the built-up pressure in the combustion chamber and the gas pressure of the pre-filled supply chamber. By opening the bursting diaphragm and, resp., by this abrupt pressure compensation a shock wave is formed which runs along the longitudinal axis of the inflator through the supply chamber at high velocity so as to open a closure means, preferably a bursting disk, by local excess pressure on a front-side end of the supply chamber. After that inflating gas, especially a mixture of the gas generated by the combustion of the fuel and the gas stored in the supply chamber in a pressurized state can exit the inflator via a diffuser so as to flow into an inflatable airbag, for instance. Due to bursting of the bursting diaphragm in the activated state of the inflator, an enlarged discharge opening can be generated so that gas generated by burning the fuel can flow more quickly into the supply chamber and through the same out of the inflator. Due to the generation of the shock wave, the closure means or the bursting disk, resp., of the supply chamber can be opened more quickly than with inflators that form no shock wave in the case of function. 
     Moreover, it is possible to arrange a combustion chamber screen, preferably in line with the predetermined breaking contour of the bursting diaphragm and with the bursting diaphragm. A combustion chamber screen can withhold possible combustion particles which may be formed by the combustion of the fuel, especially the solid fuel. 
     Further it is of advantage to arrange the igniter and the bursting diaphragm and/or the combustion chamber screen and/or the predetermined breaking contour of the bursting diaphragm and/or the bursting disk on the longitudinal inflator axis. With the aid of such arrangement optimum ignition of the fuel, especially of the solid fuel, and/or the compressed gas as well as efficient formation and propagation of the shock wave and thus destruction of the bursting diaphragm and/or bursting disk is achieved. Finally, this serves for a save and quick functioning of the inflator. For example, molds pressed into tablet shape can be used as solid fuel. 
     The through hole has at least an opening width, especially a diameter of 0.5 to 3.00 mm, especially of 1.4 mm. The through hole has at least such opening width that for producing the inflator when the inflator is filled with gas pressure compensation between the gas supply chamber and the combustion chamber takes place in less than 15 seconds, especially in less than 10 seconds, especially in less than 8 seconds, especially in less than 5 seconds. The opening width and the diameter of the through hole, in other words, is at least so large that upon production of the inflator after build-up of the combustion chamber rapid pressure compensation from the gas supply chamber into the combustion chamber is reached, the clock cycle especially amounting to 5 seconds. 
     Moreover, the through hole, especially the opening width can be configured so that upon activation of the inflator an increase in pressure takes place in the combustion chamber so as to cause the bursting diaphragm to open. In other words, the opening width and, resp., the diameter of a through hole are not allowed to be configured too large so that the configuration of the shock wave and, resp., the functional opening of the bursting diaphragm is not impaired. Despite the existing through hole a significant increase in pressure must be allowed to be formed in the combustion chamber so that the bursting diaphragm can be destroyed or opened according to its function. 
     Summing up, the opening width and, resp., the diameter of a through hole has to be designed between two parameters having a contrary effect. These are the required pressure increase in the combustion chamber and the pressure compensation between the gas supply chamber and the combustion chamber. 
     It is further possible that in the inflator inside the gas supply chamber additional fuel is accommodated for re-supplying hot gas. In other words, apart from the fuel provided in the combustion chamber of the inflator, there can be further stored additional fuel in the gas supply chamber which can be ignited after opening the bursting diaphragm and/or after forming the shock wave and thus can serve as additional source for hot gas for assistant filling later in time of an inflatable airbag. 
     In this case the additional fuel can be provided in the gas supply chamber loosely and/or in packed or packaged form, wherein the chemical composition and/or the geometric design of the additional fuel can be different from the fuel in the combustion chamber. 
     Especially the additional fuel can be a fluid, in particular a gaseous ignitable fuel. 
     As regards an airbag module, the object is achieved by the features of claim  13 . Accordingly, an airbag module includes a bursting diaphragm according to the invention and/or an inflator according to the invention. 
     As regards a vehicle safety system, the object is achieved by the features of claim  14 ; accordingly the vehicle safety system includes a bursting diaphragm according to the invention and/or an inflator according to the invention and/or an airbag module according to the invention. The vehicle safety system may be a vehicle occupant restraint system, for example an airbag and/or a seat belt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features of the invention are resulting from the following description of plural variants with respect to the enclosed drawing, in which: 
         FIG. 1  shows a schematic cross-section across an inflator according to the invention; 
         FIG. 2  shows a perspective view of a bursting diaphragm according to the invention; and 
         FIGS. 3 to 5  show views of predetermined breaking contours configured according to the invention. 
     
    
    
     DESCRIPTION 
       FIG. 1  shows an inflator  10  comprising an elongate cylindrical housing  11  forming the external housing of the inflator  10  on the first axial end of which an igniter  12  is provided and on the second axial end of the housing  11  a diffuser  13  is provided. The diffuser  13  is provided with discharge orifices and is adjacent to the housing  11  in the axial direction and guides the outflowing gas to a place of action, for example an inflatable airbag not shown here. 
     A bursting diaphragm  14  divides the housing  11  into a combustion chamber  15  and a gas supply chamber  16 . In the direction of the longitudinal inflator axis L the combustion chamber  15  is connected to the igniter  12  in the housing  11 . In the combustion chamber  15  a predetermined amount of fuel not shown is provided. This fuel can be present in the form of tablets, for example. 
     In the direction of the longitudinal inflator axis L the supply chamber  16  is adjacent to the combustion chamber  15 . The supply chamber  16  is filled with gas, especially cold gas (for instance argon, helium or an appropriate gas mixture). The bursting diaphragm  14  does not close the gas supply chamber  16  in a pressure-tight manner against the combustion chamber  15  so that a flow communication exists between the two chambers  15  and  16 . For this reason, when producing the inflator  10  upon filling the gas supply chamber  16  with gas, especially cold gas, this gas flows via through holes of the bursting diaphragm  14  also into the combustion chamber  15 , until pressure compensation between the two chambers  15  and  16  is reached. Preferably the pressure compensation is brought about within approx. 5 seconds. Prior to activating the inflator  10 , hence compressed gas is provided both in the gas supply chamber  16  and in the combustion chamber  15  in mutual flow communication. 
     In the variant of the inflator according to the invention shown here, the bursting diaphragm  14  according to the invention is press-fitted or clamped in the housing  11 . However, the bursting diaphragm  14  can also be connected to the housing  11  by material connection. 
     In the area in which the bursting diaphragm  14  is fastened in the housing  11  the latter includes an annular peripheral notch  17 . To the inside of the notch  17  the outer surface of the bursting diaphragm  14  is adjacent so that the bursting diaphragm  14  is supported in the area of the notch  17  and the bursting diaphragm  14  thus is additionally secured. In case that the bursting diaphragm  14  is connected to the housing  11  by material connection, the annular peripheral notch  17  can be dispensed with, wherein the housing in this area can have an equally continuous cylindrical shape. 
     In order to withhold combustion particles, for instance, a combustion chamber screen  18  can be inserted ahead of the bursting diaphragm  14  in the combustion chamber  15 . 
     Upon activation of the inflator  10 , the igniter  12  receives an electric signal for activating the same or for igniting the fuel. The ignition of the fuel provided in the combustion chamber  15 , especially solid fuel, results in a sudden increase in pressure in the combustion chamber  15  so that the predetermined breaking contour of the bursting diaphragm  14  not shown in  FIG. 1  is destroyed or opened so that an opening, which is large related to the diameter of the housing  11 , is suddenly formed in the bursting diaphragm  14 . This abrupt opening generates a shock wave that enters into the gas supply chamber  16  and passes through the same up to the bursting disk  19 , as described in the foregoing. 
     In the shown embodiment of an inflator  10  according to the invention the igniter  12 , the combustion chamber screen  18  and the bursting diaphragm  14  are located on the longitudinal inflator axis L. In this way optimum ignition of the fuel present in the combustion chamber  15  is obtained so that an efficient formation and propagation of the shock wave is reached. The inflator shown here can be used, for example, for inflating especially an airbag, and/or in a belt tensioner system. 
     It is further possible that in the inflator  10  inside the gas supply chamber  16  an additional fuel not shown is accommodated for re-supplying hot gas. 
     In  FIG. 2  a possible embodiment of a bursting diaphragm  14  is illustrated. The bursting diaphragm  14  substantially has the shape of a cap including a flat lid  23 . The outer contour  26  of the bursting diaphragm  14  is first formed by a cylindrical circumferential wall  20  as well as a beveling  21 . Another segment of the outer contour or of the shell surface or of the entire circumferential wall is adjacent to the beveling  21 . This is the frusto-conical circumferential wall  22  to which the flat lid  23  is connected. 
     As illustrated in  FIG. 1 , the combustion chamber screen  18  is located completely inside the bursting diaphragm  14 , the combustion chamber screen  18  being adjacent to the inside of the beveling  21 . The bulges of the bursting diaphragm  14  and of the combustion chamber screen  18  are formed in opposite direction. 
     In the lid  23  of the bursting diaphragm  14  a predetermined breaking contour  24  is incorporated. The predetermined breaking contour  24  is C-shaped according to the embodiment of  FIG. 2 . Moreover, there two through holes  25  are provided, wherein the through holes are formed on the end points  27  of the predetermined breaking contour  24 . The areas of a geometric shape or line or arc-shaped contour are referred to as end points  27 . The through holes  25  prevent bursting diaphragm parts from being separated upon opening or tearing the bursting diaphragm  14 . In other words, the through holes  25  have a hinge or tear stop function. As already afore-mentioned, the through holes  25  allow cold gas to pass upon filling the gas supply chamber  16  during production of an inflator. In the present case the through holes  25  are circular and have a diameter of 0.5 to 3.0 mm, especially of 1.0 to 2.5 mm, especially of 1.2 to 2.0 mm, especially of 1.4 mm. 
     The cross-section of the through hole  25  is sufficiently small so as to permit an increase in pressure in the combustion chamber  15  up to a specific bursting of the bursting diaphragm  14  in the case of operation, i.e. upon activation of the inflator. 
     The predetermined breaking contour is preferably formed by stampings and/or millings and/or notches and/or laser abrasions, the residual wall thickness in the area of the stampings, for example, exhibiting a smaller material thickness than the shell surface or outer contour  26  and the stampings in the non-activated state of the inflator not breaking through. The bursting pressure of the predetermined breaking contour  24  can be adjusted very accurately and in a reproducible manner by the number, length and depth of the stampings. 
     Upon activation of the inflator  10  the predetermined breaking contour  24  tears so that a relatively large opening is formed which preferably extends to more than half of the entire diameter of the housing  11 . 
       FIG. 3  merely illustrates the lid  23  of a bursting diaphragm  14  and the top view thereof, respectively. The predetermined breaking contour  24  incorporated in the lid  23  is cross-shaped in the present case. The cross-shaped predetermined breaking contour  24  is formed by two perpendicular lines or predetermined breaking lines  28 . The two predetermined breaking lines  28  have the same length and intersect in center. Through holes  25  are formed on the end points  27  of the two predetermined breaking lines  28 . 
     The diameters or cross-sections of the through holes  25  are equal. In other words, all through holes  25  of the bursting diaphragm  14  have the same opening width. When the four configured through holes  25  are connected a square is formed. In other words, the through holes  25  are the corner areas or corners of an imaginary square. Upon activation of the inflator and related destruction or opening of the predetermined breaking contour  24 , the predetermined breaking lines  28  rupture so that triangular lid segments  29  are folding outwardly and thus form an opening in the lid  23 . Consequently, this folding of the lid segments  29  forms a square or approximately square opening from which the shock wave is formed or introduced in the gas supply chamber  16  not shown here. 
     In  FIG. 4 , too, the lid  23  of a bursting diaphragm  14  and the top view thereof are shown. In the lid  23  a predetermined breaking contour  24  is incorporated. In the shown example the predetermined breaking contour  24  is formed of three predetermined breaking lines arranged in H shape. On the end points  27  of the predetermined breaking lines  28  arranged in parallel respective through holes  25  are formed. Also in this case, the through holes  25  are arranged relative to each other so that they form the corners of an imaginary square. By tearing or breaking the predetermined breaking lines  28  two rectangular lid segments  29  are bulged outwardly so that they in turn form an opening in the lid  23  of the bursting diaphragm  14 . 
     The predetermined breaking contour  24  formed in the lid  23  according to the embodiment of  FIG. 5  is formed by two predetermined breaking arches  30 . The predetermined breaking contour is thus formed in double C shape. The predetermined breaking arches  30  especially have a semicircular design. On the end points  27  of the two predetermined breaking arches  30  through holes  25  are formed which in turn constitute the corners of the square in an imaginary square. Upon activation of the inflator  10  or upon breaking of the predetermined breaking contour  24 , two semicircular lid segments are outwardly bulged and form an enlarged opening in the bursting diaphragm  14 . 
     The inflators, airbag modules and vehicle safety systems according to the invention are provided with bursting diaphragms  14  according to the invention in accordance with the embodiments illustrated in  FIGS. 2 to 5 . 
     LIST OF REFERENCE NUMERALS 
     
         
           10  inflator 
           11  housing 
           12  igniter 
           13  diffuser 
           14  bursting diaphragm 
           15  combustion chamber 
           16  gas supply chamber 
           17  notch 
           18  combustion chamber screen 
           19  bursting disk 
           20  cylindrical circumferential wall 
           21  beveling 
           22  frusto-conical circumferential wall 
           23  lid 
           24  predetermined breaking contour 
           25  through hole 
           26  outer contour 
           27  end point 
           28  predetermined breaking line 
           29  lid segment 
           30  predetermined breaking arch 
         L longitudinal inflator axis