Patent Document

FIELD OF THE INVENTION 
     The invention relates to a pyrotechnic means for vehicle occupant protection systems including a container for an ignitor, propellant and/or compressed gas. 
     BACKGROUND OF THE INVENTION 
     Pyrotechnic means in the field concerned are known wherein an electrically actuated ignitor is surrounded by a solid propellant which is capable of spontaneous combustion on being ignited. The resulting hot gas serves, for instance, to ignite further propellant charges or directly for inflating a gas bag or for tensioning a seat belt. Also known are pyrotechnic means wherein an electrically actuated ignitor is surrounded by a minor quantity of solid propellant and ignitor and propellant are arranged within a container filled with compressed gas. Ignitor and propellant serve on ignition to open a bursting diaphragm provided in the container and in subsequent exit of the compressed gas to compensate the losses in temperature and pressure thereof during a specific time span. Typically the container for ignitor, propellant and/or compressed gas is press fitted with a mounting so that ambient effects such as e.g. moisture are kept away from the interior of the container. If the container is required to be gas-tight, for example 0.5% loss in 15 years at 220 bar helium, the container needs to be sealed by complicated and expensive methods, such as e.g. glass potting the joints, due to welding or soldering being prohibitive in view of the high temperatures involved which would otherwise damage or detriment the ignitor, propellant or compressed gas. 
     It is the intention of the invention to facilitate production of gas-tight pyrotechnic means having long-term stability. 
     SUMMARY OF THE INVENTION 
     For this purpose in accordance with the invention a pyrotechnic means is provided for vehicle occupant protection systems including a container for an ignitor, a propellant and/or compressed gas wherein the container includes a container body and at least one container lid and a gas-tight ultrasonic welded joint is provided between the container body and the container lid. This ultrasonic welded joint is gas-tight and in addition has long-term stability. Due to the contact surface areas between container body and container lid being heated up only locally due to friction in ultrasonic welding the remainder of the container remains more or less cold so that ignitor, propellant or compressed gas are not heated up, or merely insignificantly so, during ultrasonic welding. It has been surprisingly discovered that during ultrasonic welding the heating up fails to be propagated to the inner walls in contact with the propellant. 
     In one aspect of the invention the container body and/or the container lid are made of a non-ferrous heavy metal or an alloy of non-ferrous heavy metal. Using a non-ferrous heavy metal or an alloy of non-ferrous heavy metal offers good conditions for ultrasonic welding between container body and container lid. For example, the application of Cu 99.5, a bronze alloy, or a brass alloy is possible. Preferably a soft material is employed for the container lid and a harder material for the container body. A harder material for the container body promotes a controlled bursting action of a bursting diaphragm provided in the wall thereof. 
     In an advantageous manner, container body and/or container lid can also be made of aluminium or an aluminium alloy. Container and container lid are preferably made of Al 99.5−99.75 or an aluminum alloy such as e.g. AlMgSi 0.5. 
     In another aspect the container body comprises a peripheral wall, the face surface area of which locates the container lid. Configuring the container body in this way results in an arrangement of advantage for ultrasonic welding. Due to the desired high surface area pressure during welding the contact surface area between container body and container lid is maintained as narrow as possible, for example &lt;1 mm. 
     It is of advantage when the face surface area of the peripheral wall is chamfered in the direction of the container opening and the container lid rests against the face surface area and the chamfer. As a result, the container lid is centered in place simply by being mounted on the container body due to the container lid then being in contact with the face surface area and chamfer. Welding is done in the region of the face surface area and in the region of the chamfer or only in one of the two regions. With the container and the container lid being configured like this, it is possible especially with thin-walled containers to prevent lateral buckling of the peripheral wall in case of welding pressure applied from above by lateral support of the peripheral wall. 
     It is likewise of advantage when the container body comprises a peripheral flange on which the container lid is mounted. Also in the case of very thin-walled containers this creates a contact surface area of sufficient stability for an ultrasonic weld. In addition to this a peripheral flange can be well supported, so that the desired surface area pressure during welding can be produced in a simple manner. 
     In yet a further aspect of the invention it is provided for that a bursting diaphragm is formed in the container body and/or the container lid. Such a bursting diaphragm simplifies production of the pyrotechnic means since no separate bursting diaphragm needs to be connected gas-tight to the container body or the container lid. 
     In still another aspect of the invention the region of the bursting diaphragm is surrounded by a notch. As a result, a controlled bursting response of the bursting diaphragm is made possible once a predetermined internal pressure has been attained. 
     In a final aspect of the invention it is provided for that the region of the bursting diaphragm is offset. Offsetting of the bursting diaphragm may be done, for example, by drawing down. It is likewise possible to produce the complete container lid or container body including the bursting diaphragm by cold extrusion or deep drawing. Offsetting the bursting diaphragm results in strain-hardening of the offset portion so that the bursting diaphragm bursts as defined or is punctured by the internal pressure, instead of bulging in part and bursting without control like a soft material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention read from the following description and from the drawing to which reference is made and in which: 
     FIG. 1 is a section view of the container of a first embodiment of a pyrotechnic means in accordance with the invention, 
     FIG. 2 is a section view of the container in a second embodiment, 
     FIGS. 3 to  6  are section views of various aspects of the contact region between container lid and container body, 
     FIG. 7 is a section view of a further embodiment of the pyrotechnic means in accordance with the invention, 
     FIG. 8 is a side section view taken along the line VIII—VIII of FIG. 7, 
     FIG. 9 is a section view of a further embodiment of the pyrotechnic means in accordance with the invention, 
     FIG. 10 is a side section view taken along the line X—X of FIG. 9, 
     FIG. 11 illustrates one possibility of sealing a cable leadthrough, and 
     FIG. 12 is a partial section view of a container suitable for tube installation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1 there is illustrated a rotationally symmetrical container  10  of a pyrotechnic source of compressed gas. The container  10  serves to receive a propellant charge which is ignited by a conventional ignitor (not shown) arranged outside of the container burning through one wall of the container  10  The container  10  consists of a container body  12  and a container lid  14 , both made of aluminum and contacting each other at annular contact surface areas  16  and  18  where they are ultrasonically welded gas-tight. One such rotationally symmetrical container may be arranged upstream of a piston in a cylinder of a belt tensioner, for instance. A Bowden cable necessary for tensioning the belt then extends through the middle of the toroidal container  10 . The container lid  14  comprises at its outer rim a cranked portion supporting the face surface area of the outer peripheral wall  20  of the container body  12 . The inner rim of the container lid  14  locates a raised face  22  configured on the inner peripheral wall  24  of the container body. 
     In this arrangement the container body  12  and container lid  14  thus circumscribe an annular inner space provided to receive the propellant  26 . To weld the container body  12  and container lid  14  to each other, after the propellant has been filled, the container body  12  is supported by its underside and a pressure oriented downwards as shown in FIG. 1 is exerted on the container lid  14  in the region of its outer and inner rim so that an even surface area pressure is produced at the peripheral contact surface areas  16  and  18 . At the same time the container body  12  and container lid  14  are caused to vibrate at least in the region of the contact surface areas  16  and  18  so that they are moved relative to each other horizontally as shown in FIG.  1 . The vibration frequency in this region is in the ultrasonic range and the amplitude is of the order of 30 μm. Due to the surface area pressure and the relative movement in the region of the contact surface areas  16 ,  18  this region is heated up strongly, resulting in a weld joint. In this arrangement the heating up is restricted substantially to the region of the contact surface areas  16  and  18  so that the remaining regions of the container body  12  and container lid  14  remain more or less cold. As regards gas-tightness the weld features substantially the same properties as the base material of the container body  12  and of the container lid  14  so that excellent properties are achieved without the need for any additional sealing measures. 
     The wall thickness of the peripheral wall  20  of the container body  12  is less than that of the remaining walls and than that of the container lid  14  so that, for one thing, a fast burn-through of the peripheral wall  20  can; be achieved by the ignitor being arranged outside of the container and, for another, the peripheral wall  20  is the first to burst following ignition of the propellant  26  within the container  10 . 
     Referring now to FIG. 2 there is illustrated a section view of a container  30  of a second embodiment of the invention. Like the embodiment as shown in FIG. 1 a container body  32  and a container lid  34  define an annular interior space for receiving the propellant. The container lid  34  comprises a bursting diaphragm  36  which is offset meaning positioned on a different plane, relative to the surface of the container lid  34 , as shown in FIG. 2, and is surrounded by a notch  38 . The wall thickness of the container lid  34  is greatly reduced in the region of the bursting diaphragm  36  so that the bursting diaphragm  36  is the first to burst on ignition of the propellant in the container  32 . In producing the container lid  34 , for instance by cold extrusion, the region of the burst diaphragm  36  is strain-hardened to thus burst in a more defined response than would be in the case of a softer material. 
     Referring now to FIG. 3 there is illustrated a section view of the outer rim portion of a container  40  which in turn consists of a container body  42  and a container lid  44 . The container body  42  comprises a peripheral flange  46  supporting the rim portion of the container lid  44 . For welding the flange  46  and the rim portion of the container lid  44  to each other, they are pressed together and caused to vibrate horizontally to each other in the ultrasonic range as indicated by the arrows in FIG. 3. A bursting diaphragm  47  configured in the peripheral wall of the container body  42  is burnt through by a conventional ignitor arranged outside, and a peripheral notch  48  in the container lid  44  ensures a controlled bursting response of the container  40  following ignition of the propellant in the container  40 . The bursting diaphragm  47  formed in the container body  12  is surrounded by a notch. 
     Referring now to FIG. 4 there is illustrated a container  50 , wherein for the ultrasonic welding between container body  52  and container lid  54  the face surface area of an outer peripheral wall  56  of the container body  52  is provided. 
     Referring now to FIG. 5 there is illustrated a further container  60  comprising a container body  62  and a container lid  64 . The container lid  64  is cranked at right angles in its outer rim portion to thus be reliably supported by the container body  62 . 
     Referring now to FIG. 6 there is illustrated section wise a container  70 , the container body of which comprises an outer peripheral wall  72  supporting a container lid  74 . The face surface area  76  of the peripheral wall  72  is chamfered in the direction of the container opening, as a result of which a chamfer  78  is formed. Complying with the angle of inclination of the chamfer  78  the container lid  74  is cranked so that it rests against both the face surface area  76  and the chamfer  78 . A uniform ultrasonic weld is achieved in the region of the face surface area  76  and of the chamfer  78  by pressure being exerted on the container body  72  and the container lid  74  in the direction of the arrows as evident in FIG.  6 . As a result, more particularly, mere localized welding at the points of contact is avoided, i.e. instead a full surface area gas-tight weld being achieved. 
     Referring now to FIGS. 7 and 8 there is illustrated a further embodiment of a pyrotechnic source of compressed gas in accordance with the invention. The pyrotechnic means as shown in FIGS. 7 and 8 is configured as an ignitor  80  provided for igniting a conventional propellant charge for a conventional belt tensioner (not shown). The ignitor  80  is arranged on a tubular inflator  82  in which a propellant charge (not shown) is located and which is held in contact with the inflator  82  by a clamping ring  84 . The ignitor  80  comprises a container comprising a container body  86  and a container lid  88 , both made of aluminum and produced as deep drawn or cold extruded parts. Arranged within the container is a squib  90  comprising a filament  92  connecting two electric leads  94  to each other. The electric leads  94  are embedded in a plastic body  96  which together with ferromagnetic components  98  is inserted in the container body  86 . In the region of the squib  90  the container body  86  comprises a projection  100  including a booster charge  102  inserted in an opening of the inflator  82  and the thin wall of which can be penetrated on ignition. Container body  86  and container lid  88  are secured and sealed to each other by an ultrasonic weld joint. 
     Referring now to FIGS. 9 and 10 there is illustrated the situation in which the ignitor can be integrated in an gas generator  110 . In this arrangement the container consisting of the container body  112  and container lid  114  represents not only the housing of the ignitor but also that of the inflator  110 . Provided within the container in the region of the squib  116  is space for accommodating a propellant charge  118 . The container body  112  comprises in the region surrounding the squib  116 , i.e. the combustion chamber, a greater wall thickness. Container lid  114  and container body  112  are welded to each other by an ultrasonic weld, whilst the contact pins  120  extending through the container lid  114 , as continuations of the leads  122 , are sealed off conventionally, for example, with the aid of a sealing compound. 
     Referring now to FIG. 11 there is illustrated a further possibility of sealing off the leads and container lid. The container body  130  and container lid  132  are connected to each other by an ultrasonic weld. Formed protruding from the container lid  132  is a tubular sleeve  134  which is sealed off by pressing it for sealing engagement with a sleeve  136  of the electric leads  138 . 
     Referring now to FIG. 12 there is illustrated sectionwise a container  140  which has been ultrasonic welded in the region of its peripheral flange as evident from FIG. 12 a . In this arrangement the peripheral flange permits simple and reliable ultrasonic welding whilst causing problems in installing the container in a tube. If the container  140  is thus installed, for example, in the tube of a belt tensioner, the peripheral flange, as shown in FIG. 12 b , is bent up. The container  140  can then be inserted into a tube without problems.

Technology Category: 7