Abstract:
The invention relates to an actuator assembly for an airbag module in a vehicle safety system comprising an actuator ( 10 ) and a tensioning means ( 20 ), wherein the actuator ( 10 ) includes a release member ( 12 ) which in the idle state of the actuator is connected to a retaining member ( 11 ) and is separable from the retaining member ( 11 ) by actuating a pyrotechnical ignition unit of the actuator ( 10 ) along a predetermined breaking point ( 13 ) so as to release a loop ( 23 ) of a tensioning means ( 20 ). The invention excels by the fact that the loop ( 23 ) is formed between two tensioning means portions ( 21, 22 ) which are interconnected directly at the predetermined breaking point ( 13 ) by a connecting means ( 30 ) such that the loop ( 23 ) is tensioned around the predetermined breaking point ( 13 ) in a self-fixing manner. Furthermore the invention relates to an airbag module, a vehicle safety system and a manufacturing method.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to an actuator assembly for an airbag module in a vehicle safety system. Furthermore, the invention relates to an airbag module and a vehicle safety system comprising such actuator assembly as well as a manufacturing method. An actuator assembly according to the preamble of claim  1  is known, for example, from EP 1 683 690 A1. 
         [0002]    The actuator assembly known from EP 1 683 690 A1 (especially FIG. 17) comprises an actuator in the form of an explosive stud fastened at a housing of an inflator. A loop formed by a cord is laid around the actuator and is part of a retaining means adapted to be actively released upon a signal. Those retaining means or so called tethers are required to control vent holes of an inflatable airbag. 
         [0003]    In practice, tethers are frequently tensioned transversely or obliquely across an airbag. The tether therefore does not basically act perpendicularly to the longitudinal axis of the actuator. This may entail the drawback that the tether can easily be displaced inadvertently along the longitudinal axis of the actuator or can slip off the actuator, before the ignition unit of the actuator has being triggered as specified. 
         [0004]    In order to prevent the loop from slipping along the actuator and in this way the release of the loop from being obstructed when the actuator is activated, EP 1 683 690 A1 teaches to provide a clamping means for the cord or the loop. The clamping means is configured in the form of an ignition tablet plug independent of the actuator assembly. When the actuator assembly is mounted, the clamping means is plugged in the vicinity of the loop into the inflator, after the loop has been laid around the actuator, so that the clamping means is in form closure with the actuator, thereby the loop being virtually clamped. 
       SUMMARY OF THE INVENTION 
       [0005]    It is the object of the invention to state an actuator assembly for an airbag module in a vehicle safety system which ensures reliable operation and has a simple structure with compact dimensions. Furthermore, it is the object of the invention to provide an airbag module for a vehicle safety system comprising such actuator assembly, a vehicle safety system comprising such airbag module and/or such actuator assembly as well as a manufacturing method. 
         [0006]    According to the invention, this object is achieved with respect to the actuator assembly by the subject matter of claim  1 , with respect to the airbag module by the subject matter of claim  7 , with respect to the vehicle safety system by the subject matter of claim  9  and with respect to the manufacturing method by the subject matter of claim  11 . 
         [0007]    The invention is based on the idea to state an actuator assembly for an airbag module in a vehicle safety system comprising an actuator and a tensioning means, the actuator including a release member which in the idle state of the actuator is connected to a retaining member and is separable from the retaining member by activation of a pyrotechnic ignition unit of the actuator along a predetermined breaking point so as to release a loop of a tensioning means. According to the invention, the loop is formed between two tensioning means portions which are interconnected directly at the predetermined breaking point by a connecting means such that the loop is tensioned around the predetermined breaking point in a self-fixing manner. The term “idle state of the actuator” has to be understood in this context so that the actuator was not yet activated as specified, i.e. is provided in a home position in which no situation for release of the tensile means is given yet which might trigger activation of the actuator. The term “activation of the pyrotechnical ignition unit” is to be understood so that the pyrotechnical ignition unit is ignited by an, especially electric, signal which starts up the activation of the actuator. 
         [0008]    The loop tensioned around the predetermined breaking point in a self-fixing manner ensures that the tensioning means remains in the area of the predetermined breaking point at the actuator. Thus it is sufficient to merely provide a flat notch in the area of the predetermined breaking point which retains the loop in its position. It is provided for this purpose that immediately or directly at the predetermined breaking point a connecting means is provided for interconnecting the two tensioning means portions delimiting the loop of the tensioning means along the tensioning means. The connecting means is arranged so closely to the predetermined breaking point that the loop is tensioned around the predetermined breaking point in a self-fixing manner and free from play, respectively. Thus the loop is fixed in the axial direction of the retaining member or release member, resp., substantially via the frictional force between the actuator and the tensioning means. Therefore, the loop is frictionally fixed in the axial direction of the actuator. This results advantageously in the fact that the wall thickness of the actuator can be reduced. The actuator assembly according to the invention therefore has especially small outer dimensions. Moreover, in the invention compared to the afore-mentioned EP 1 683 690 A1 a costly clamping device requiring large space in the form of an ignition tablet plug to be separately mounted at an inflator can be dispensed with. Rather, the invention states a simple solution including a connecting means which is solely engaged in the loop itself formed between two tensioning means portions, thereby the loop being tensioned in a self-fixing manner, virtually in itself. 
         [0009]    According to a preferred embodiment of the actuator assembly according to the invention, the loop is preformed, especially prefixed by the connecting means. In this case the loop is already existing or already formed, before the tensioning means is connected to the actuator during manufacture of the actuator assembly. Advantageously, the loop has an, especially natural, diameter which is smaller than the diameter of the actuator in the area of the predetermined breaking point. This ensures that after connecting the loop to the actuator, there is a frictional force between the actuator and the predetermined breaking point, resp., and the loop, said frictional force securing the loop in the axial direction of the actuator. 
         [0010]    In this case the tensile means forming the loop is further preferred to be elastic so that the loop can be elastically expanded. Hence the actuator can be inserted in the loop and the loop can automatically tighten around the actuator. For forming a pre-fabricated loop the connecting means is designed at the two tensioning means portions preferably as seam, clip, especially stapler clip or metallic clip, shrink hose and/or seal. In other words, the loop can be formed between tensioning means portions which are interconnected in a fixed, especially non-detachable or not non-destructively detachable manner. In this way, it is additionally ensured that the loop is held to be closely adjacent around the actuator in the long run. 
         [0011]    Basically different connecting means can be employed. For example, the connecting means can be a seam. The tensioning means portions thus can be sewn directly in the area of the predetermined breaking point so as to form a closely adjacent loop between them. 
         [0012]    A similar effect can be achieved by a clip. The clip can be a stapler clip or generally a metallic clip and can encompass or reach through the tensioning means portions. Especially the tensioning means portions can be stapled together so that the clip extends through the tensioning means portions and fixes the latter to each other. 
         [0013]    Furthermore, for fixing the tensioning means portions a seal can be provided which prevents destruction-free opening of the loop. The seal can completely enclose the areas of the tensioning means portions at which it is arranged. 
         [0014]    Another embodiment of the invention provides that when manufacturing the actuator assembly the loop is formed or fixed only after looping or winding the tensioning means around the actuator. The actuator assembly thus can have a postfixed loop, i.e. the loop is postfixed by the connecting means. The connecting means can be especially in the form of a cable tie or an adhesive tape for forming a postfixed loop. A postfixed loop can also be realized by a connecting means in the form of a clip or seal. In general, for forming a postfixed loop the connecting means is adapted to encompass the tensioning means portions, especially to be laid around the tensioning means portions or to reach through the same, when the tensioning means portions are arranged in parallel to each other. 
         [0015]    The connecting means can also be a shrink hose or an, especially elastic, O-ring. By such connecting means a combined preformed and postfixed loop can be formed. It is especially provided that although the loop is formed by slipping on the shrink hose or the O-ring already before connection to the actuator, it is initially variable as regards the loop diameter, however. Only after the loop is laid around the predetermined breaking point of the actuator and is tensioned free from play, is the loop or the diameter of the loop, resp., fixed by the connecting means. When using a shrink hose, it can be moved tightly toward the predetermined breaking point and can subsequently be heated so that the loop contracts tightly around the actuator and the predetermined breaking point, respectively. When using an O-ring, the elasticity thereof causes the pretensioning force which permits tightly enclosing the actuator with the tensioning means or the loop, respectively. 
         [0016]    Preferably the tensioning means includes an elastic material at least in the area of the loop so that the loop can be expanded, especially temporarily radially extended for mounting on the predetermined breaking point. This applies in particular to embodiments including a prefixed loop or a tight connection of the tensioning means portions. In general, an elastic design of the tensioning means, at least in the area of the loop, is useful for all embodiments. The actuator can be inserted in the loop so that the loop is positioned in the area of the predetermined breaking point. As soon as the force extending the loop subsides, the loop contracts around the actuator and thus is automatically fixed. It is especially provided in this context that in the relaxed, i.e. non-mounted, state the loop has a smaller cross-sectional diameter, especially measured at the radial inside of the loop cross-section, than the predetermined breaking point. 
         [0017]    Furthermore, the ratio of the first distance, measured between the longitudinal axis of the actuator assembly and the connecting means, from a second distance, measured between the longitudinal axis and the outer diameter of the loop, amounts to a value of up to 1.3, especially up to 1.2, especially up to 1.1, especially up to 1.0, further especially up to 0.9. Inadvertent displacement of the loop along the actuator can be realized by positioning the connecting means as closely as possible to the loop, i.e. closely to the outer diameter of the loop. As regards optimum positioning, appropriate tests have resulted in the afore-mentioned setting ratios, i.e. the ratio of the first distance from the second distance. In other words, a sufficiently good self-fixing of the loop is still reached when the first distance is up to 30% larger than the second distance (ratio value of up to 1.3). It is also possible that the connecting means is positioned so far in the direction of the longitudinal axis of the actuator assembly that the first distance is smaller than the second distance, i.e. the connecting means virtually covers an area of the outer loop diameter (ratio value of up to 0.9). 
         [0018]    According to an independent aspect, the invention is based on the idea to state an airbag module for a vehicle safety system comprising an airbag, an inflator and an afore-described actuator assembly. The afore-mentioned actuator assembly is especially suited for use in an airbag module. 
         [0019]    In a preferred configuration of the airbag module according to the invention, it is provided that the tensioning means is connected to the airbag. In particular, the tensioning means can be fastened to an inner wall and/or an outer wall of the airbag. The tensioning means thus can be used in combination with the actuator to vary the volume of the airbag as needed. For example, the tensioning means can be connected to venting flaps so that gas can escape from the airbag by activating the actuator unit and releasing the tensioning means. The tensioning means can also be connected to the inner wall of the airbag so that the airbag can expand to a larger volume by release of the tensioning means after activation of the actuator. 
         [0020]    Another independent aspect of the invention relates to a vehicle safety system comprising an afore-described airbag module and/or an afore-described actuator assembly. In the vehicle safety system preferably an electric trigger unit is provided which is signal-connected to the actuator assembly so that an electric trigger pulse can be transmitted to the ignition unit. Further, the vehicle safety system according to the invention can have at least one sensor for detecting vehicle movement data which is connected to the trigger unit. The trigger unit can be adapted to the actuator assembly, especially the ignition unit, for transmitting the electric trigger pulse as a function of the measured vehicle movement data. 
         [0021]    Furthermore, within the scope of the application a method for manufacturing an afore-described actuator assembly and/or an afore-described airbag module and/or an afore-described vehicle safety system is disclosed and claimed in which the tensioning means is laid around the predetermined breaking point so as to form the loop. Subsequently, the tensioning means portions are interconnected in the area of the predetermined breaking point so that the loop tightens around the predetermined breaking point in a self-fixing manner. Alternatively, the tensioning means includes an elastic loop through which the release member of the actuator assembly is passed so that the loop is positioned at the predetermined breaking point and contracts around the predetermined breaking point in a self-fixing manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Hereinafter the invention shall be illustrated in detail by way of embodiments with reference to the enclosed schematic figures, in which: 
           [0023]      FIG. 1  shows a perspective view of the actuator assembly of the invention according to a preferred embodiment, wherein the loop is fixed by a shrink hose as connecting means; 
           [0024]      FIG. 2  shows a partly cut view of the actuator assembly according to  FIG. 1 ; 
           [0025]      FIG. 3  is a perspective view of an actuator assembly according to the invention in accordance with another preferred embodiment, wherein the loop is fixed by an O-ring as connecting means; 
           [0026]      FIG. 4  is an actuator assembly of the invention according to another preferred embodiment, wherein the loop is fixed by a clip as connecting means; 
           [0027]      FIG. 5  shows a perspective view of an actuator assembly of the invention according to another preferred embodiment, wherein the loop is fixed by a seal as connecting means; and 
           [0028]      FIG. 6  shows a longitudinal sectional view of an actuator assembly of the invention according to a preferred embodiment, wherein the relation between the diameter of the tensioning means and the groove depth is visible at the predetermined breaking point of the actuator. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    Each of the following embodiments shows an actuator assembly comprising an actuator  10  including a pyrotechnic ignition unit. The pyrotechnic ignition unit is connectable or connected to a trigger unit not shown via an electric connection  15 . The actuator  10  is formed of a retaining member  11  and a release member  12  which are interconnected. Especially, the retaining member  11  and the release member  12  can be coupled in one part. Between the retaining member  11  and the release member  12  a predetermined breaking point  13  is arranged which is preferably in the form of a groove  14 . By activating the pyrotechnic ignition unit the release member  12  can be blasted off the retaining member  11 , wherein the actuator  10  is separated at the predetermined breaking point  13 . 
         [0030]    A tensioning means  20  which is part of the actuator assembly is arranged around the actuator  10  in the area of the predetermined breaking point  13 . The tensioning means  20  can be a rope, a cord or a tether, for example. The tensioning means  20  comprises or forms a loop  23  which is wound or guided around the actuator  10 . The loop  23  extends in a groove  14  forming the predetermined breaking point  13 . By separating the release member  12  from the retaining member  11  the loop  23  can be released. In this way a one-sided fixation of the tensioning means  20  can be undone. 
         [0031]    In order to minimize the dimensions of the actuator  10  it is preferred when the groove  14  has a small groove depth. In order to guarantee nevertheless that the loop  23  is retained in the area of the predetermined breaking point  13 , especially does not laterally slip and cannot be inadvertently displaced along the longitudinal axis M of the actuator, it is provided that the loop is tensioned around the predetermined breaking point  13  in a self-fixing manner, preferably free from play. 
         [0032]    The loop  23  is formed in that two tensioning means portions  21 ,  22  are interconnected immediately at the predetermined breaking point  13  by a connecting means  30 . The connecting means  30  is arranged so closely at the predetermined breaking point  13  that the loop  23  tightens closely and substantially free from play around the actuator  10 , especially around the predetermined breaking point  13 . For this purpose different connecting means  30  can be used. 
         [0033]    By the term “immediately” in accordance with the invention it is understood that the loop  23  is laid around the substantially circular ring-shaped predetermined breaking point  13  or groove  14  so tightly that it has equally a substantially circular ring-shaped form. The inner diameter of the loop  23  is thus smaller than the outer diameter of the retaining member  11  and the release member  12 , respectively. 
         [0034]      FIG. 1  shows an embodiment in which the tensioning means portions  21 ,  22  are interconnected by a shrink hose  31 . The shrink hose  31  can be slipped over the tensioning means portions  21 ,  22  with the loop  23  prior to wrapping the actuator  10 . After that, the actuator  10  is inserted in the loop  23  formed in this way and is positioned in the area of the loop  23  with its predetermined breaking point  13 . Then the shrink hose  31  is guided closely to the predetermined breaking point  13  and is heated so that the shrink hose  31  contracts. Consequently also the loop  23  contracts and encloses the predetermined breaking point  13  in a self-fixing manner and free from play. Especially the loop  23  is pulled into the groove  14  which can be comparatively small, especially having a small depth. The groove  14  primarily, especially exclusively, serves for determining the position of the loop  23 . The loop  23  is axially secured by the frictional connection between the loop  23  and the predetermined breaking point  13  resulting from the pretension exerted by the loop  23 . 
         [0035]    In the partly cut view according to  FIG. 2  the close positioning of the loop  23  in the groove  14 , i.e. in the area of the predetermined breaking point  13 , is clearly visible. It is also evident that the distance between the connecting means  30  and the groove  14  and the groove bottom, respectively, corresponds approximately to the diameter D of the tensioning means  20 . As described already in the foregoing, it is equally expressed hereby that the two tensioning means portions  21 ,  22  are interconnected by the connecting means  30  immediately at the predetermined breaking point  13 . It is ensured in this way that the loop  23  is tensioned around the actuator  10  free from play. 
         [0036]    An alternative connecting means  30  is shown in  FIG. 3 . The tensioning means portions  21 ,  22  are connected to an O-ring  32  in this embodiment. The O-ring  32  can initially be slipped over the tensioning means portions  21 ,  22  similarly to a shrink hose  31 , before the actuator  10  is subsequently inserted in the loop  23 . The O-ring  32  then is guided or rolled closely to the predetermined breaking point  13  or groove  14 , wherein the O-ring  32  tightly contracts the tensioning means portions  21 ,  22  due to its elasticity. As a consequence, also the loop  23  contracts tightly and is finally adjacent to the predetermined breaking point  13  free from play. 
         [0037]      FIG. 4  illustrates another option of fixing the tensioning means portions  21 ,  22 . In this embodiment a clip  33  is used as connecting means  30  which reaches through the first tensioning means portion  21  and the second tensioning means portion  22  and thus fixes the same to each other. The clip  33  can be used for forming a preformed and prefixed loop  23 . This means that the clip  33  fixes the tensioning means portions  21 ,  22  to each other before the actuator  10  is inserted in the loop  23 . Thus the diameter of the loop  23  is defined already prior to mounting at the actuator  10 . It is advantageous in this case when the tensioning means  20  includes an elastic material at least in the area of the loop  23  so that the loop  23  is elastically expandable for being positioned above the predetermined breaking point  13 . As soon as the loop  23  is arranged in the area of the predetermined breaking point  13 , the expanding force for the loop  23  is released so that due to its elastic properties the loop  23  contracts in a self-fixing manner, especially free from play, and tightens around the predetermined breaking point  13 . 
         [0038]    Alternatively, the clip  33  can be set only after the actuator  10  has been inserted in the loop  23 . Hence the tensioning means  20  can first be laid or wound around the actuator  10 , especially in the area of the predetermined breaking point  13 . Subsequently the clip  33  is set, wherein the tensioning means  20  is kept tensioned. The clip  33  in this way fixes the pretensioning force exerted on the loop  23  by the tensioning means  20 . The loop  23  is thus frictionally connected to the predetermined breaking point  13  and is frictionally retained in the groove  14 , respectively. 
         [0039]    Instead of a clip  33  a seal  34  can be used, as is exemplified in  FIG. 5 . The effect of the seal  34  corresponds to the effect of the clip  33 . In this way the seal  34  can be used both for a preformed and prefixed loop  23  and for a postfixed loop  23 . It is also possible that a preformed and postfixed loop  23  is formed with the aid of the seal  34 . For this purpose the seal  34  can have a through-opening through which the tensioning means portions  21 ,  22  are guided. In this way, between the tensioning means portions a loop  23  is formed which can be laid around the actuator  10 . The seal  34  is compressed so as to fix the tensioning means portions  21 ,  22  only when the loop  23  is closely adjacent to the predetermined breaking point  13 . The preformed loop  23  is thus postfixed. 
         [0040]      FIG. 6  illustrates the advantages of the actuator assembly according to the invention. By connecting the connecting means  30  in this manner to the tensioning means portions  21 ,  22 , especially at a distance from the predetermined breaking point  13  which approximately corresponds to the diameter D of the tensioning means  20 , a self-fixing frictional connection is obtained between the tensioning means  20  and the actuator  10 . This is also applicable especially when the tensioning means  20  acts obliquely on the actuator  10 . In this case, too, it is expressed, as described already in the foregoing, that the two tensioning means portions  21 ,  22  are interconnected directly, in accordance with the invention, at the predetermined breaking point  13  by the connecting means  30 . 
         [0041]    The frictional connection or the self-fixing support, resp., of the loop  23  in the area of the predetermined breaking point  13  prevents axial slipping or inadvertent displacement of the loop  23 . Therefore, in the actuator assembly according to the invention it is sufficient to provide a comparatively small groove depth T. In particular, the groove depth T can be smaller than the cross-sectional radius of the tensioning means  20 . In this way the total diameter of the actuator  10  is reduced. Hence the outer dimensions of the actuator  10  are independent of the dimensions of the tensioning means  20 . Moreover, in this way the geometry of the actuator  10  is facilitated. As a consequence, the requirements to the tools used for manufacturing the actuator  10  are reduced, which in total reduces the manufacturing costs and the manufacturing efforts. 
         [0042]    Furthermore,  FIG. 6  shows a longitudinal axis M of the actuator assembly extending through the center of the elongate actuator assembly and in rotationally symmetric actuator assemblies also forming the axis of symmetry thereof. A first distance A 1  is measured, starting from the longitudinal axis M to the connecting means  30 . A second distance A 2  is measured, starting from the longitudinal axis M to the outer diameter of the loop  23 . The distances A 1  and A 2  defined here relate to the completely mounted state of the actuator assembly, as shown in  FIG. 6 , i.e. after fixing the loop  23  around the predetermined breaking point  13  by means of the connecting means  30 . 
       LIST OF REFERENCE NUMERALS actuator 
       [0000]    
       
           11  retaining member 
           12  release member 
           13  predetermined breaking point 
           14  groove 
           15  electric connection 
           20  tensioning means 
           21  first tensioning means portion 
           22  second tensioning means portion 
           23  loop 
           30  connecting means 
           31  shrink hose 
           32  O-ring 
           33  clip 
           34  seal 
         D diameter of tensioning means 
         T groove depth 
         M longitudinal axis 
         A 1  first distance 
         A 2  second distance