Abstract:
A side airbag unit for mounting on or in the backrest of a vehicle seat includes an airbag skin enclosing a gas chamber, and an inflator for filling of said gas chamber. The airbag skin exhibits a main section which serves for protection of the vehicle occupant when the side airbag is expanded and which in the resting state of the side airbag is present as a package, wherein the package is at least partly rolled. In order to provide a side airbag unit of low weight with its airbag skin nevertheless showing a controlled and reproducible expansion behavior, the airbag skin further comprises at least one auxiliary section which in the resting state encompasses the main section in two layers at least in sections, wherein an additional area of the gas chamber is present between the two layers of the auxiliary section at least in the resting state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 U.S. National Stage of International Application No. PCT/EP2010/002969, filed May 14, 2010. This application claims priority to German Patent Applications No. DE 10 2009 042 594.2, filed Sep. 24, 2009, and DE 10 2009 023 177.3, filed May 29, 2009. The disclosures of the above applications are incorporated herein by reference. 
     TECHNICAL FIELD OF THE INVENTION 
     The invention relates to a side airbag unit for mounting in or on a backrest of a vehicle seat. 
     So-called side airbags are known in the field of vehicle construction and are used for protection of the vehicle occupants in case of a side impact. In most applications, the side airbag inflates between the person to be protected and the side structure of the vehicle. Two basic designs are known in this connection: 
     PRIOR ART 
     In a first basic design it is possible to locate the side airbag unit which exhibits the side airbag and an inflator—mostly a gas generator—in the side structure of the motor vehicle. The side airbag has two side walls, wherein when the side airbag is inflated, one side wall points towards the occupant and one points towards the side structure of the motor vehicle, so that the one side wall forms the impact surface and the other side wall forms the support surface. The deployment direction of the airbag is basically horizontal in the direction of travel. 
     The second design is more common. Here, the side airbag unit is located in the backrest of the vehicle seat and is connected with the frame of the backrest by means of an inherently stable mounting part. The airbag which is used here also exhibits two side walls, wherein the one side wall forms the impact surface. If only a small amount of space exists between the side cheek of the backrest and the side structure, and if the side airbag is made sufficiently thick, the second side wall of the side airbag comes into contact with the side structure of the vehicle in an accident situation, and this side structure therefore forms a support surface. If this cannot be ensured, the mounting part often exhibits a section lying on the outside, which supports the side airbag. Such a design, however, means that the mounting part is of not inconsiderable weight, which is naturally disadvantageous. 
     Various folding and/or rolling methods are known, how the airbag skin can be rolled and/or folded to a package. These different methods naturally have an influence on the manner of unfolding of the airbag skin, and therefore particularly have an influence on how aggressively the expanding airbag acts on the vehicle occupant. Because of a quite low aggressive effect on the vehicle occupant, particularly when the occupant is not in his standard sitting position (out of position), an outer roll (or out board roll) is often preferred. 
     In order to save weight, side airbags without a rigid, housing-type retaining part have in the meantime become known. With these, however, there is generally the problem that it is difficult to set the expansion behaviour of the airbag skin as desired. In particular in the case of the outer roll mentioned above, in the absence of a housing-type retaining part it can happen that the unfolding airbag skin catches or snags on the door cladding. In order to prevent this, rolled airbag packages have become known which additionally exhibit at least one fold. However, circumstances might occur in which the unfolding is not perfectly reproducible. 
     Generic patent application US 2006/0145459 A1 shows a side airbag unit whose airbag skin is specially folded in order to achieve an improved unfolding behaviour. 
     SUMMARY OF THE INVENTION 
     Starting from this, the invention sets itself the problem to improve the state of the art in such a way that the side airbag unit can be formed with low weight and its airbag skin nevertheless shows a controlled and reproducible expansion behaviour. 
     The side airbag unit exhibits an airbag skin enclosing a gas chamber and an inflator for filling the gas chamber. Within this arrangement, the airbag skin has a main section, which—when the airbag is expanded—serves for the protection of the vehicle occupant and which, in the resting state of the airbag skin is present in form of a package, wherein the package is at least partially rolled. According to the invention, the airbag skin also exhibits an auxiliary section, which in the resting state at least in sections encompasses the main section in two layers, wherein at least in the resting state an area of the gas chamber is located between the two layers of the auxiliary section. 
     By means of the measure according to the invention, the gas chamber of the side airbag exhibits an additional area in addition to the main area at least during an early expansion phase. This additional chamber supports and guides the main area during this phase. When the side airbag is fully expanded, the additional area generally no longer needs to be separated from the main area, which means that an airbag skin with very simple geometry can be used. The airbag skin can in particular be woven in one piece or can be manufactured of two cuttings connected by means of a edge seam, without additional seams or similar being necessary in the area of the transition between main area and the additional area of the gas chamber. Therefore the time and effort needed for manufacture is not or is not basically different from the time and effort needed for a conventional airbag skin for a side airbag, and also the weight basically corresponds to the weight of a conventional airbag skin. In addition, the rolling of the airbag skin into a package can be kept very simple and an additional fold is usually not necessary. 
     None of the above measures makes a significant contribution to the weight of the side airbag unit, so that the objective of weight reduction is achieved. 
     In a first preferred configuration, the auxiliary section encompasses the package from the outside, viewed from the vehicle seat, such that the additional area expands at an early stage of the deployment between the main area of the gas chamber and the side structure of the vehicle and thus directs the unfolding main section of the airbag skin away from the inner structure and prevents the main section of the airbag skin from getting stuck at the inner structure. In this configuration it is in most cases preferred to roll the package of the main section to the outside, leading to a “gentle” deployment behaviour regarding the occupant. 
     In a second preferred configuration, the auxiliary section encompasses the package from the inside, viewed from the vehicle seat, such that the additional area expands at an early stage of the deployment between the main area of the gas chamber and the frame and/or cushioning of the vehicle seat and thus directs the unfolding main section of the airbag skin away from the occupant and prevents the main section of the airbag skin from “shooting” against the occupant. In this configuration it is in most cases preferred to roll the package of the main section to the inside in order to prevent the main section from getting stuck at the inner structure of the vehicle. 
     So, one can see that in most cases it is to be preferred that the rolling direction of the main section corresponds to the position of the auxiliary section. If the main section is rolled to the outside, the auxiliary section encompasses the package at the outside and vice versa. But it needs to be emphasized that for special purpose applications it is also possible that rolling direction of the package of the main section and the position of the auxiliary section are the other way: If the main section is rolled to the outside, the auxiliary section encompasses the roll at the inside and vice versa. 
     In a preferred embodiment, a fabric section follows on from the auxiliary section, so that the auxiliary section and the fabric section completely encompass the package and therefore hold the package together in its rolled condition, so that the auxiliary section has a dual function. 
     In a second embodiment of the invention the airbag skin comprises two auxiliary sections, with a first auxiliary section encompassing the package from the outside, viewed from the vehicle seat and a second auxiliary section encompassing the package from the inside, viewed from the vehicle seat. 
     Further advantageous embodiments result from the further subclaims and from the embodiments now described in relation to the drawings. The drawings show: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of first and second cuttings for an airbag skin in accordance with the present teachings. 
         FIG. 2  is a view of a side airbag unit of the present teachings including the cuttings of  FIG. 1  and a gas generator. 
         FIG. 3  is a simplified sectional view taken along the line A-A of  FIG. 2 . 
         FIG. 4  is a simplified sectional view similar to  FIG. 3 , after folding of an auxiliary section of the airbag skin. 
         FIG. 5  is a view of the side airbag unit taken in the direction of Arrow B in  FIG. 4 . 
         FIG. 6  is a view corresponding to  FIG. 4  showing the side airbag unit ready to install. 
         FIGS. 7   a - 7   e  are a series of views following ignition of the gas generator. 
         FIG. 8  is a simplified horizontal section through a backrest of a vehicle seat illustrating the side airbag in the state shown in  FIG. 7   e.    
         FIG. 9  is a view similar to  FIG. 6  showing the side airbag unit in a second, ready to install configuration. 
         FIG. 10   a - 10   d  are a series of view of the side airbag unit of  FIG. 9  after ignition of the gas generator. 
         FIG. 11  is a view of three cuttings for another airbag skin in accordance with the present teachings. 
         FIG. 12  is a view of a side airbag unit including the cuttings of  FIG. 11  and a gas generator. 
         FIG. 13  is a simplified sectional view taken along the line A-A of  FIG. 12 . 
         FIG. 14  is a simplified sectional view similar to  FIG. 13 , shown after folding of an auxiliary section of the airbag skin. 
         FIG. 15  is a view corresponding to  FIG. 14  showing the side airbag unit ready to install. 
         FIG. 16  is a prior art view of a side airbag unit operatively associated with a vehicle seat. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First the state of the art will be described again with reference to  FIG. 16 .  FIG. 8  shows a horizontal section through the backrest  12  of a vehicle seat  10 , on whose frame  16  a side airbag unit  20  is mounted. The side airbag unit  20  comprises an airbag skin  22 , a gas generator  70  serving as inflator and a housing-type retaining part  60  located in the side cheek  14  of the backrest  12 , and being connected with the frame  16 . The housing-type retaining part  60  has a U-shaped cross-section with three legs  62 ,  64 ,  66 . 
     The retaining part  60  has three legs, namely the first leg  62 , the second leg  64  and the third leg  66 . Within this arrangement, the third leg  66  is the outer leg and among others has the task of guiding the airbag skin  22  while it is unfolding upon ignition of the gas generator  70 . For which purpose the third leg—and therefore housing  60  as a whole—has to be formed relatively stable and therefore heavy. 
       FIG. 1  shows two cuttings  80 ,  90  for an airbag skin of a side airbag. Both cuttings  80 ,  90  have a mushroom-like shape with a first section  82 ,  92  having an approximately oval shape and a second section  84 ,  94 , following on from the first section. This second section is considerably narrower than the first section and is approximately rectangular. It can be seen that the two first sections  82 ,  92  of both cuttings  80 ,  90  are congruent, while the second section  84  of the first cutting  80  is somewhat longer than the second section  94  of the second cutting  90  and has a set break line  87  in the form of a perforation, and two fixing holes  86 . In addition, two through-holes  85  are provided in the first cutting  80 . Often, a further opening is present for insertion of the gas generator into the finished sewn airbag skin. As this does not contribute to the understanding of the present invention, this is not shown here. 
       FIG. 2  shows a side airbag unit  20 , which comprises an airbag skin  22 , which is sewn from the two cuttings  80  and  90  just described, and a gas generator  70  serving as inflator. The two cuttings  80 ,  90  just described are connected with each other by means of the edge seam  95 , so that the two cuttings enclose a gas chamber  40 . This gas chamber is divided in accordance with the shape of the cuttings into a main area  42  and an additional area  44 , wherein the gas generator  70  is located in main area  42 , but near to the transition to additional area  44 . The edge seam  95  exhibits two interruptions  96  in the front area, which form outflow openings. Because the second section  84  of first cutting  80  is longer than the second section  94  of the second cutting  90 , a section of the first cutting extends beyond the gas chamber  40 . This section is referred to as fabric section  50 , or in more general terms as flexible section. In the embodiment shown, this fabric section  50  is therefore formed in one piece with the first cutting  80  of the airbag skin  22 , which is to be preferred but not obligatory. It would also be possible that the fabric section  50  is a separate cutting sewn to the first cutting  80 . From  FIG. 2  it can also be seen that the set break line  87  is located in this fabric section  50 , in other words outside the gas chamber  40 . 
       FIG. 3  shows a section along section A-A through the airbag unit  20  from  FIG. 2 . In this representation, the main area  42  of gas chamber  40  is located to the left of the gas generator  70 , and the additional area  44  is located to the right of it. In the same way as the gas chamber  40  can be divided into a main area  42  and an additional area  44 , it is also possible to divide the sections of the airbag skin  22  into a main section  24  and an auxiliary section  30 , wherein the main section  24  is formed by the first section  82  of the first cutting  80  and the second section  92  of the second cutting  90  and the auxiliary section  30  is formed by a part of the second section  84  of the first cutting  80 , namely by the part which overlaps with the second section  94  of the second cutting  92 , and the second section  94  of the second cutting  90 . The gas generator bolts  72  extend through the through-holes  85 . 
       FIG. 4  shows how the auxiliary section  30  of the airbag skin  22 —and therefore also the fabric section  50 —is folded over towards the front, so that it lies in front of the main section  24 . 
       FIG. 5  shows the items shown in  FIG. 4  in a birds-eye view from Direction B. It should be emphasized at this point, that for reasons of weight reduction it is mostly to be preferred to form the auxiliary section narrower (this means in installed state with less height) than the main section. However, this is not obligatory. The shape shown in the embodiment, however, has the advantage that less fabric surface and a relatively low gas volume are needed, which means that only a correspondingly small gas generator is necessary. 
       FIG. 6  shows airbag skin  22 , which was just described, in a state prepared for installation in a vehicle in a representation corresponding to  FIG. 4 . The main section  24  of the airbag skin  22  is fully rolled-in—no additional folding takes place—, wherein the roll points in the direction of the auxiliary section  30 . Auxiliary section  30  and fabric section  50  together encompass the main section  24  rolled into a package, wherein the auxiliary section  30  and the fabric section  50  each encompass approximately around half of the package. The fixing openings  86  are hung into the gas generator bolts  72 . Therefore the auxiliary section  30  and the fabric section  50  also serve as a cover holding the package together. In the state shown in  FIG. 6 , the additional area  44  and the main area  42  of the gas chamber  40  form almost separate chambers. 
       FIG. 7   a  shows the side airbag unit  20  shown in  FIG. 6 , which is fixed to a retaining part  60 , which in turn is carried by a frame  16  running in a side cheek  14  of the backrest  12  of a vehicle  10 . In principle, a direct mounting on the frame  16  could also be envisaged, which, however, is seldom to be preferred for practical reasons. 
       FIG. 7   b  shows the items shown in  FIG. 7   a  immediately after the ignition of the gas generator  70 . It can be seen that the additional area  44  of the gas chamber  40  fills very rapidly with gas and therefore guides the early expansion of the unrolling main section  24  of the airbag skin  22 . In particular, the additional area  44  of the gas chamber  40  (which is enclosed by the auxiliary section  30  of the airbag skin  22 ) prevents the main section  24  of the airbag skin  22  from expanding too strongly in the direction of the side structure of the vehicle, to which the main section  24  would tend because of its direction of rolling. 
       FIG. 7   c  shows the items shown in  FIG. 7   b  at a somewhat later point in time. It can be seen here that the border between the additional area  44  and the main area  42  of the airbag  40  is beginning to disappear, so that it is no longer possible to differentiate precisely between the main section  24  and the auxiliary section  30  of the airbag skin  22 . 
       FIG. 7   d  shows the items represented in  FIG. 7   c  at a later point in time. Here, the border between the main area  42  and the additional area  44  of the gas chamber  40  has completely disappeared, however a thickening of the gas chamber  40  remains in the area in which the additional area  44  was located. 
       FIG. 7   e  shows the items represented in  FIG. 7   d  following complete unfolding of the airbag. 
       FIG. 8  shows the airbag unit in a state as shown in  FIG. 7   d  mounted to the frame  16  of the backrest  12  of a vehicle seat  10 . One can see that the retaining element  60  has no housing-type structure since no such housing-type structure is needed order to direct the airbag during deployment. 
     In the embodiment shown above, the main section  24  of the airbag skin  22  is rolled to the outside in the resting state of the airbag. But it needs to be emphasized that the invention can also be applied to a side airbag whose main section is rolled to the inside. 
     The  FIGS. 9 to 10   d  show a second configuration of an airbag unit whose airbag skin is very similar to the one of the embodiment shown in  FIGS. 1 to 8 . Here, the main section  24  of the airbag skin is rolled to the inside and the additional area  44  of the gas chamber is located between the retaining part  60 /frame  16  of the back rest and the main area  42  of the gas chamber. So, at the beginning of the deployment ( FIGS. 10   a  to  10   c ) the main section  24  of the airbag skin is pushed away from the back rest and thus from the occupant. The inboard roll of the main section  24  of the airbag skin prevents the main section  24  from getting stuck to the interior structure of the vehicle (not shown). 
     In both preferred configurations described above, the rolling direction of the package of the main section of the airbag skin is against the auxiliary section (if the main is rolled to the outside (outboard roll), the auxiliary section encompasses the package from the outside, if the main section is rolled to the inside (inboard roll), the auxiliary section encompasses the package from the inside). In case of deployment this leads to an unrolling of the package of the main section against the auxiliary section which is in most applications essential, as described. In the sense of this application, the term “rolled against” means this kind of configuration. 
     Instead of having only one auxiliary section of the airbag skin (which is sufficient in the most applications) it is also possible to have two auxiliary sections such that the package of the main section is encompassed from both sides. A possible embodiment is shown in the  FIGS. 11 to 15 : 
     The airbag skin is comprised of three cuttings, with the first two cuttings  80 ,  90  basically having the mushroom-like shape of the cuttings of the first embodiment. The third cutting  100  is basically of rectangular shape with the height of the rectangle corresponding to the height of the second sections  84 ,  94  of the first and second cutting  80 ,  90  and the length being basically double the length of the second sections  84 ,  94  ( FIG. 11 ). 
     The airbag skin is closed with a first seam  102  connecting the thirst sections  82 ,  92  of the thirst and the second cutting  80 ,  90  and a second seam  104  connecting the third cutting  100  to the second sections  84 ,  94  of the first and the second cutting  80 ,  90  ( FIGS. 12 and 13 ). As in the first embodiment, the main area  42  of the gas chamber is enclosed between the first sections  82 ,  92  of the first and the second cutting  80 ,  90 . The additional areas  44 ′,  44 ″ are enclosed between the second sections  84 ,  94  and the third cutting  100  ( FIG. 14 ). 
       FIG. 15  shows how the rolled package of the main section of the airbag skin is encompassed by the two auxiliary sections  30 ′,  30 ″ from both sides. 
     LIST OF REFERENCE NUMBERS 
     
         
           10  Vehicle seat 
           12  Backrest 
           14  Side cheek 
           16  Frame 
           20  Side airbag unit 
           22  Airbag skin 
           24  Main section 
           30  Auxiliary section 
           30 ′ first auxiliary section 
           30 ″ second auxiliary section 
           40  Gas chamber 
           42  Main area 
           44  Additional area 
           44 ′ first additional area 
           44 ″ second additional area 
           50  Fabric section 
           60  Retaining part 
           62  First leg 
           64  Second leg 
           66  Third leg 
           70  Gas generator 
           72  Gas generator bolt 
           80  First cutting 
           82  First section 
           84  Second section 
           85  Through-hole 
           86  Fixing hole 
           87  Set break line (perforation) 
           90  Second cutting 
           92  First section 
           94  Second section 
           95  Edge seam 
           96  Interruption in seam 
           100  third cutting 
           102  first seam 
           104  second seam