Abstract:
An airbag module including a first casing enclosing a first gas space, a first inflator and a control device for controlling ventilation of the first gas space or the shape of the first casing. The control device includes a second casing ( 42 ) enclosing a second gas space and a gas source. The second gas space is bordered by a permanent edge connection, and further includes a control element such as a strap ( 60 ), whose first end is connected to the first casing and whose second end is sewn to the second casing ( 42 ) by a tear seam ( 49 ), and is decoupled from the second casing ( 42 ) upon filling of the second gas space. The tear seam ( 49 ) touches or intersects the edge connection at two points so that the tear seam divides the second gas space into two regions ( 43   a,    43   b ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. 10 2014 000 185.7, filed on Jan. 14, 2014 and PCT/EP2015/050375, filed on Jan. 12, 2015. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an airbag module for a motor vehicle, including a control device. 
       BACKGROUND 
       [0003]    Nearly every airbag, in particular every motor vehicle front impact airbag, includes a ventilation device through which inflation gas can escape from the airbag internal gas space—hereinafter called the first gas space—for restraint of the person to be protected. The first gas space is enclosed by the outer casing of the airbag, so that kinetic energy of the person to be protected is dissipated and the person to be protected does not simply rebound from the airbag casing of the airbag. In the simplest case such a ventilation device is simply a vent opening, in particular a vent opening in the airbag casing. 
         [0004]    In order to take into account different accident situations and/or the weight of the person to be protected, control devices for influencing the shape of the airbag or the pressure in the gas space are known in the prior art. If the shape of the airbag is to be controlled, a releasable catch strap may be provided as a part of the control device. Furthermore, adaptive ventilation devices are known, which in addition to the vent opening include a throttle element, which in a first state throttles the gas flow through the vent opening more intensely than in a second state. Generally the first state is the throttled, or even fully closed state, and the second state is the less-throttled, for example, completely open state. 
         [0005]    U.S. Pat. No. 6,648,371 B2 shows an example of an active control device wherein a pyrotechnically functioning actuator is described as part of the control device. Here the first end of a strap is connected to the throttle element and the second end of this strap to a bolt of the actuator. The actuator is thereby held, in particular, on the housing base of the airbag module. As long as the actuator is not actuated, the throttle element is thus connected to the housing base via the strap. In the event of a completely expanded airbag casing, the strap comes into a taut state, which holds the throttle element in its first state. If the actuator is actuated, then the bolts or fasteners that hold the second end of the strap are jettisoned by a pyrotechnic charge, the strap loses its tension, and the throttle element transitions into its second, namely its unthrottled (or less throttled) state. In principle this technology functions very well, but has the disadvantage that parts, such as, for example, the bolts, can fly about inside the gas space of the airbag casing, and that hot gases are created inside the airbag casing due to the pyrotechnic charge. Furthermore the pyrotechnic charge feeds additional gas into the gas space of the airbag casing, which is not always desired. 
         [0006]    WO 2014/001317 A1 shows a similarly functioning actuator. Here an ignition capsule is surrounded by a hose. The end (usually upper end) of the hose facing away from the actuator is closed by a tear seam. This tear seam also holds the second end of a strap. If the ignition capsule is ignited due to an electrical signal, the tear seam tears, whereby the initially closed end of the hose opens and the second end of the strap is released. The advantage here is that no bolts or the like can fly about in the interior of the airbag. However, here the gas of the ignition capsule is also fed into the gas space of the airbag. 
         [0007]    The generic device described by DE 10 2005 039 418 B4 proposes an airbag module including an adaptive ventilation device, wherein the control device includes a “small airbag module inside the airbag module” having a casing (second casing) and a gas source. Here the throttle element is influenceable by the second casing. The casing of this second airbag—designated hereinafter as the second casing—encloses a second gas space which can be filled by the gas source configured in particular as an ignition capsule. If this happens, then the second casing filled with gas withdraws the throttle element in the form of a cloth away from the vent opening so that the ventilation device transitions into its second, unthrottled state. It is advantageous here in particular that the gas generated by the ignition capsule remains in a second gas space. It is disadvantageous here that the second casing and vent opening must be directly adjacent to each other, which is often very difficult to realize. In particular it is scarcely possible to dispose the vent opening in the airbag casing in such a manner. 
       SUMMARY AND INTRODUCTORY DESCRIPTION 
       [0008]    On this basis a feature of the present invention is to further develop an airbag of the above-described type such that great structural and functional flexibility. In the case that the ventilation is to be actively controlled, it should be possible in particular to provide the vent opening in one section of the airbag. This airbag casing can be the outer casing, which separates the first gas space from the environment, or a partition casing, which separates two chambers from each other. This casing is designated in summary form below as the “first casing.” 
         [0009]    This above described feature is achieved by an airbag module having the features described herein. 
         [0010]    In addition to the second casing, the control device in accordance with the present invention includes a control element whose first end is at least indirectly permanently connected to the first casing, and whose second end is sewn to the second casing when the second gas space is not filled, and decoupled from the second casing when the second gas space is filled. In order that the tear seam can withstand high tensile forces when the second gas space is not filled and is nevertheless destroyed during filling of the second gas space (so that the second end of the control element releases from the second casing), it intersects or touches the edge connection at two points so that the tear seam divides the unfilled gas space into two regions divided by the tear seam. 
         [0011]    As in the generic DE 10 2005 039 418 B4, the second casing remains closed so that no (or at least very little) gas of the gas source (second ignition capsule) reaches the second gas space. Nevertheless, due to the division of the second gas space by the tear seam, a very great opening force is generated, which has the advantage that when the second gas space is not filled, the tear seam can support very large forces and a ripping of the tear seam nevertheless occurs. Especially good results can be achieved here if the tear seam is configured as U-, omega-, W-, or V-shaped, in particular in the region where it is sewn to the control element, so that a large seam length results. However, other geometric designs of the tear seam, in particular a meander-shaped design, are also possible. Here it is generally to be preferred that the tear seam intersects the edge of the control element at exactly two points since the reproducibility is thereby improved. 
         [0012]    In some embodiments of the present invention the control element is a strap; however it is also conceivable to sew a covering element of a ventilation opening, in particular in the form of a nozzle, directly to the second casing. 
         [0013]    Due to the large forces that can be transmitted between the second casing and the control element when the second casing is not filled, both a use of active controlling of an adaptive ventilation device and an active controlling of the airbag depth (dual depths) are possible with the present invention. 
         [0014]    The second casing described herein is advantageously manufactured from a one-piece blank, wherein the casing can also be configured as multi-layer sections to increase the volume and to increase the stability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Further preferred embodiments are indicated from the other dependant claims as well as from the exemplary embodiments depicted in more detail with reference to the Figures. 
           [0016]      FIG. 1  shows an exemplary embodiment of an airbag module in accordance with the present invention in a schematized cross shows sectional depiction in the rest state, 
           [0017]      FIG. 2  the depiction in  FIG. 1  after ignition of the gas generator and filling of the first gas chamber, which is enclosed by the airbag casing, referred to here as the first casing, wherein, however, the ventilation device is still in a throttled state, 
           [0018]      FIG. 3  shows the depiction in  FIG. 2  after activation of an actuation unit, whereby the ventilation device is transitioned into an unthrottled state, 
           [0019]      FIG. 4  shows the actuation unit from  FIG. 2  in a plan view from direction R, 
           [0020]      FIG. 5  shows an alternative design of the actuation unit from  FIG. 4  in a depiction corresponding to  FIG. 4 , 
           [0021]      FIG. 6 a - d    show alternative designs of the connection between strap and second casing, 
           [0022]      FIG. 7 a    shows a blank for manufacturing a two-layer second casing, 
           [0023]      FIG. 7 b    shows the second casing manufactured from the blank shown in  FIG. 7   a,    
           [0024]      FIG. 8 a    shows a blank for manufacturing a four-layer second casing, 
           [0025]      FIG. 8 b    shows the second casing manufactured from the blank shown in  FIG. 8 a   , and 
           [0026]      FIG. 9  shows a second application of an inventive actuation unit in a depiction corresponding to  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The invention is first described using an application example wherein ventilation of an airbag is controlled. 
         [0028]      FIGS. 1 to 3  show a front airbag module, namely a driver airbag module for installation in the hub region of a steering wheel. It is basically constructed as in a common design and includes a housing  20  including a housing wall  20   b  and a housing base  20   a,  wherein the airbag casing designated here as first casing  10  is folded in the rest or normal non-deployed state. This first casing  10  encloses a first gas space  13 . The first casing  10  is held on the housing base  20   a  by a retaining ring  26 . A first inflator, namely a gas generator  30 , serves to fill the first gas space, which gas generator  30  in the exemplary embodiment shown extends through an opening  22  in the housing base  20   a  into the interior of the housing  20  and thus into the first gas space  13 . This gas generator  30  includes a propellant  32  in the usual manner, which is ignited by a first ignition capsule (initiator)  34  as soon as this is electrically activated via an ignition cable  36 . In the upper region of the gas generator  30  there are escape openings for the generated gas; this region of the gas generator  30  is spanned by a diffusor  24 . In the exemplary embodiment shown the connection between gas generator  30  and housing base  20   a  is effected via a flange  38  of the gas generator and damper  39 . 
         [0029]    On the first casing  10  an adaptive ventilation device  11  is provided, via which the first gas space  13  can be vented. A second ventilation device, in particular a non-adaptive ventilation device, in particular in the shape of a hole in the first casing can also be provided. However, this is not depicted. The adaptive ventilation device  11  includes a vent opening  12  and, in the exemplary embodiment shown, a cloth or patch, which surrounds the vent opening  12  and whose one end is fixedly connected to the first casing  10 . This vent feature  14  forms the throttle element of the adaptive ventilation device  11 . A strap element is provided in the form of a strap  60  whose first end  62  encircles the end of the vent feature  14  facing away from the first casing  10  such that the vent feature  14  is pulled together if the strap is under tension, so that in this state, the ventilation device is closed or at least throttled. If the first gas space  13  is filled with gas and if the strap  60  is not under tension, then the vent feature  14  is pushed outward by the pressure prevailing in the first gas space and the ventilation device transitions into its unthrottled (or less throttled) state. Such a ventilation device is described in detail, for example, in US 2006/0071461 A1, to which reference is made here, so that the exact structure of this ventilation device need not be described in more detail. 
         [0030]    In an initial state, the second end  64  of the strap  60  is connected to an element of an actuation unit  40 . In the event of an expanded first casing  10 , the actuation unit  40  serves to transfer the ventilation device  11  (that is, the vent feature  14 ) from a first, namely throttled, into a second, namely an unthrottled, state. This actuation unit  40  is described as follows. 
         [0031]    A second ignition capsule  48  is provided from which an ignition cable, namely the ignition cable  50 , extends. The second ignition capsule  48  serves as the gas source of the actuation element  40 . Furthermore, a second casing  42  is provided, which encloses a second gas space  43 . This second gas space  43  is in fluidic connection with the gas source, which in the exemplary embodiment shown is achieved in that the second ignition capsule  48  is at least sectionally accommodated in the second gas space. However, it would also be possible, for example, to provide a gas-guiding element in the form of a tube. In any case the second casing  42  and the gas source  48  should form a gas-tight unit. The second casing  42  can be formed of normal airbag fabric. Thus in a known manner the actuation unit  40  forms a small airbag module inside the actual airbag module. The second end  64  of the strap  60  is sewn to the second casing  42  such that the seam, namely the tear seam  49 , sews together two layers of the second casing  42 . There are thus three layers in sections, namely the second end  64  of the strap  60 , as well as two layers of the second casing  42 . This is better depicted below with reference to  FIG. 4 . The structure of the second casing  42  and its connection to the strap  60  is discussed again below with reference to  FIG. 4 . 
         [0032]    If the gas generator  30  is now ignited, then gas flows into the first gas space  13  and the first casing  10  expands in the usual manner. The strap  60  thereby tenses, whereby the vent feature  14  is pulled together and very little or no gas can escape through the vent opening  12  so that the ventilation device is in a first, throttled state ( FIG. 2 ). 
         [0033]    If the second ignition capsule  48  is now ignited, then the gas generated by it fills the second gas space  43 , whereby the second casing  42  expands but remains closed. Due to this expansion, the tear seam  49  is torn and thus the second end  64  of the strap  60  is separated from the second casing  42 . The strap  60  can thus no longer support tension forces and the vent feature  14  is pushed outward by the inflation gas pressure prevailing in the first gas space, whereby the vent opening  12  is released and the ventilation device and thus also the vent feature  14  transitions into a second, namely unthrottled (or less throttled) state. As already mentioned, the second casing  42  remains closed so that the second ignition capsule  48  and the gas generated by it cannot interact with other elements of the airbag module ( FIG. 3 ). 
         [0034]      FIG. 4  shows the specific design of the second casing  42  and the connection between second casing  42  and strap  60 . In this exemplary embodiment, the strap  60  forms the control element. In the exemplary embodiment shown, the second casing is configured as two-layer; a sectional structure made from a plurality of layers is also possible as shall be seen later with reference to  FIGS. 8 a  and 8 b   . The present description applies generally, however for the sake of simplicity of vent feature description, two layers shall be discussed in the following. The two layers are sewn to each other by a permanent seam  47 . Instead of a permanent seam  47 , another permanent connection could be provided, for example an adhesive connection or a welded connection. The permanent seam  47  extends essentially pear- or omega-shaped around the second gas space  43  such that there is a relatively narrow opening  46  through which either the second ignition capsule  48 , a supply tube, or the ignition cable  50  of the second ignition capsule enters from outside into the second gas space  43 . The first alternative to that just described is depicted; here the second ignition capsule  48  passes through the opening  46  into the interior of the second casing. In the use state the pass-through opening should be closed as tightly as possible, which can be effected by a clamp, by adhering or other suitable measures. Starting from the opening  46  the second gas space  43  widens out in a pear-shaped manner. 
         [0035]    The strap  60  is sewn to the second casing  42  by the tear seam  49 , wherein the tear seam  49  extends through the second gas space  43  and divides it into a first region  43   a  and a second region  43   b.  In order to achieve this separation, the second tear seam  49  intersects the permanent seam  47  (or a corresponding other permanent connection) at two points, wherein it would also be sufficient that the tear seam starts at these two points. However, a real intersecting is to be preferred for mechanical reasons. In the region wherein the strap  60  is sewn to the second casing  42 , the tear seam  49  is configured essentially U-shaped, wherein the two arms of the U extend essentially parallel to the longitudinal extension of the strap  60 . Instead of a U-shape, a V- or omega-shape is also suitable in particular. With a very wide control element, a W-shape (this could also be called an M-shape) can also be advantageous. 
         [0036]    The first region  43   a  of the second gas space  43  is the region adjacent to the opening  46 , which region is initially filled with gas in the event of the activating of the gas source (here the second ignition capsule  48 ). Due to the relatively small volume of the first region  43   a  of the second gas space, in the event of ignition of the second ignition capsule  48  (or another supplying of gas) a large force is exerted on the tear seam  49  and in particular on the region of the tear seam  49  that connects the strap  60  to the second casing  42 , so that the tear seam is certainly torn at least in this region and the strap  60  is separated from the second casing  42 . This is supported in particular in that the region of the tear seam  49  that connects the strap  60  to the second casing  42  is disposed relatively centrally with respect to the second gas space  43 . The pear shape of the second gas space  43  also contributes to a certain tearing of the tear seam with certain maintenance of the gas-tightness of the second casing. After destruction of the tear seam  49  the second region  43   b  also fills with gas, and the first region  43   a  and second region  43   b  unite into a common, closed gas space. 
         [0037]      FIG. 5  shows a variant to that shown in  FIG. 4 ; here the strap  60  is asymmetrically disposed, wherein the section of the tear seam  49  that connects the strap  60  to the second casing  42  is also configured U-shaped with two arms parallel to the longitudinal extension of the strap  60 . The “asymmetry angle” (angle measured between the longitudinal axis of strap  60  and the axis of symmetry of second gas space  43 ) can in principle be any, in particular between 0° and 90° (similar angles are illustrated in  FIGS. 6 c  and 6 d   ). 
         [0038]      FIGS. 6 a  to 6 d    show alternative embodiments of the tear seam  49 , which here extends essentially meander-shaped. A relatively large seam length also arises here, wherein, however, the first region  43   a  of the gas space  43  is larger than the second region. After tearing of the tear seam  49 , the first region  43   a  and second region  43   b  also unite here to a common, closed gas space. The stitching of tear seam  49  can be provided at an angle to a line perpendicular to the longitudinal axis of second gas space  43 , as illustrated in  FIG. 6 b   . The angle drawn in here can also in principle be chosen as desired between 0° and 90°. 
         [0039]    However, according to the current state of knowledge the embodiment shown in  FIGS. 4 and 5  (including their variants) is a preferred one, which is justified as follows: on the one hand there is a very favorable ratio between the volume of the first and the second region for the second gas space  43 . Furthermore, the following is significant: in the embodiment of  FIGS. 4 and 5  (this would also apply to variants wherein the section of the tear seam  49  that connects the control element to the second casing is omega-, V-, W-, M-, or even N-shaped) the tear seam  49  intersects the edge of the control element at only two points. With these two points it cannot be precisely defined whether the stitch in question of the tear seam  49  still holds the control element, and if so, by what percentage. In order to keep the reproducibility high it is also favorable to provide only two such transition points (fewer is not available, since otherwise it would not be possible to divide the second gas space  43  into two sections). Furthermore, the reproducibility is all the greater the more stitches of the tear seam  49  definitely lie inside the control element, thus the longer the section of the tear seam  49  that connects the control element to the second casing  42 . Best is the combination of both, namely to provide only two transition points and to design the section of the tear seam  49 , which connects the control element to the second casing  42 , U-, W-, V-, or omega-shaped as described above so that the ratio between the number of defined connection stitches and that of the not precisely defined connection stitches is high. 
         [0040]    As has already been mentioned, it is preferred to manufacture the second casing  42  from a one-piece blank. An example of such a one-piece blank is shown in  FIG. 7 a   . It is easily recognized that the second casing  42  can be obtained by simple folding of this blank and subsequent sewing together, welding together or adhering together providing the configuration illustrated by  FIG. 7   b.    
         [0041]    In order to generate a somewhat larger volume and a strengthened edge region, the second casing  42  can also be folded from a somewhat more complex blank, as is shown in  FIG. 8 a   , wherein the depicted left half of the blank forms two additional inner layers in the edge region; i.e., that the blank here includes two breaks or voids  70  that follow the shape of the second gas space  43 . Due to such a strengthened edge region the gas-tightness of the second gas space can also be improved, i.e., the leakage can be reduced. When folded twice as shown in  FIG. 8 a   , first about the direction designated as I and second about the direction designated by II, the completed condition results as illustrated in  FIG. 8   b.    
         [0042]    In the exemplary embodiments described up to now, wherein the ventilation of the airbag is actively controlled, it would also be possible to omit the strap  60  and to sew the cloth directly to the second casing  42 . In this case the vent feature  14  would have a dual function, namely as part of the ventilation device and as control element. 
         [0043]    Up to now the invention has been described using an application where the actuation unit  40  influences the state of an adaptive ventilation device. This is one application, but other applications are also possible, in particular the influencing of the shape, in particular the depth, of the first casing. This is shown in  FIG. 9 . Here the first end  62  of the strap  60 , serving in this case as an edge band, is directly connected permanently to the first casing  10 , in particular sewn. Prior to the ignition of the second ignition capsule  48  (i.e., prior to the activation of the actuation unit  40 ) a reduced maximum expansion of the first casing thus occurs ( FIG. 9 ), after the ignition of the second ignition capsule  48 , the full maximum expansion of the first casing  10  (not shown) (“dual depth”). All previously described embodiments of the actuation unit  40  can also be used for this application. 
         [0044]    While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.