Abstract:
A device is provided for snap-fastening an airbag unit in a subassembly of a motor vehicle, especially in a steering wheel of a motor vehicle, snap-in elements that are associated with each other being provided on the airbag unit and on the subassembly of the motor vehicle. In order to be able to snap-secure an airbag unit both to a plate-shaped subassembly and to a subassembly having a lateral wall, at least one snap-in hook is provided on the airbag unit or on the subassembly of the motor vehicle, at least one pivotable plastic snap-in clip being associated therewith on the other subassembly. The snap-in hook engages with said clip in at least one section thereof when in the snap-in position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national phase application filed under 35 U.S.C. §371 of International Application PCT/EP2007/058107, filed on Aug. 6, 2007, designating the United States, which claims priority from DE 10 2006 041 734.8, filed Sep. 1, 2006, which are hereby incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a device for snap-fastening an airbag unit in a subassembly of a motor vehicle, especially in a steering wheel. 
     BACKGROUND OF THE INVENTION 
     Devices for fastening an airbag unit in a subassembly of a motor vehicle are known. For example, an airbag module in which the airbag unit has on its outside elastically deformable snap-in hooks which can engage behind latching sections on the inside of the lateral wall of the airbag housing is known from EP 1 314 621 A1. In this case, the airbag unit is introduced into the airbag housing from above. As soon as the snap-in hooks reach the region of the latching sections, the snap-in hooks slide along the latching sections, being deformed elastically in the direction of the lateral wall of the airbag unit. Upon reaching the end position of the airbag unit in the airbag housing, the snap-in hooks spring back and engage below the latching sections of the airbag housing. The airbag module is thereby fixed in the airbag housing. This device has the disadvantage that the subassembly to which the airbag unit is to be snap-fastened must have a lateral wall on which the latching sections can be arranged. It is not possible to connect the airbag unit to a flat plate. 
     A device for snap-fastening an airbag unit in an airbag housing is further known from U.S. Pat. No. 5,620,201. In this device the airbag unit has a snap-in mechanism on each opposite side. This snap-in mechanism has a housing in which is mounted a spring-loaded pin which, during installation of the airbag unit, is pressed back against the spring force by the respective lateral wall of the airbag housing and slides along the inner wall of the airbag housing until it is pressed by the spring into an opening of the airbag housing, 
     whereby the airbag unit is locked to the airbag housing. Locking to a motor vehicle subassembly which does not have lateral walls is also possible. In this case, an angled portion which has a perpendicular section replacing the lateral wall must be mounted on the subassembly for each snap-in mechanism. In the case of this device, too, therefore, a lateral wall or a corresponding substitute must be provided in order to fix the airbag unit. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to snap-fasten an airbag unit both to a plate-shaped subassembly and to a subassembly which has a lateral wall. 
     This object is achieved according to the invention by the features described hereinafter. 
     In a device for snap-fastening an airbag unit in a subassembly of a motor vehicle, especially in a steering wheel of a motor vehicle, snap-in elements which are associated with each other being provided on the airbag unit and on the subassembly of the motor vehicle, at least one snap-in hook is provided according to the invention on the airbag unit or on the subassembly of the motor vehicle. Furthermore, at least one pivotable plastic snap-in clip which engages with the snap-in hook in at least one region in the snap-in position is associated with said snap-in hook. 
     This device has the advantage that the snap-in hooks and the associated pivotable plastic snap-in clip can be arranged at any positions of the airbag unit and the subassembly of the motor vehicle. If a steering wheel on which the horn is actuated by pressing down the airbag unit is provided as the subassembly of the motor vehicle, as a result of the inventive type of snap-fastening extraneous noises are caused neither when the airbag unit is pushed down nor when it springs back. 
     The plastic snap-in clip is preferably mounted pivotably at one end, adjoining which end it has a deformable section adjacent to which is a swivelable section, a stop on the subassembly of the motor vehicle being associated with the deformable section and the region which can be engaged being provided on the swivelable section. 
     It is advantageous if a side of the deformable section associated with the stop on the subassembly of the motor vehicle and a side of the swivelable section associated with the snap-in hook extend obliquely away from one another, starting from the bearing of the plastic snap-in clip; that is, the corresponding side of the deformable section is disposed obliquely in the direction of the stop on the subassembly of the motor vehicle and the corresponding side of the swivelable section is disposed obliquely in the direction of the snap-in hook. 
     The swivelable section preferably has a greater thickness than the deformable section. 
     In an embodiment, the bearing of the plastic snap-in clip is provided on a plate-shaped subassembly of the motor vehicle or on a plate-shaped section of a subassembly of the motor vehicle which is provided with a lateral wall, at a distance from this subassembly or this section, and the deformable and swivelable sections project into an opening of this subassembly or of this section, the deformable section resting against the wall of the opening. 
     In a further embodiment, the bearing of the plastic snap-in clip is provided on at least one lateral wall of the subassembly of the motor vehicle, at a distance from this lateral wall, and the deformable section rests against the lateral wall. 
     In a first embodiment, two at least partially hollow-cylindrical bearings, into which two cylindrical projections of the plastic snap-in clip are insertable, are provided for mounting the plastic snap-in clip. The bearings are preferably open on one side in the manner of claws. 
     In a second embodiment, the bearing for the plastic snap-in clip is cylindrical and the plastic snap-in clip has a recess engaging over this bearing, which recess is at least partially hollow-cylindrical and is open on one side. 
     The snap-in hook on the airbag unit and the bearing for the plastic snap-in clip are preferably provided on the subassembly of the motor vehicle. 
     In a further configuration of the invention it is provided that the swivelable section of the plastic snap-in clip has an oblique face associated with the snap-in hook, which oblique face is disposed such that the snap-in hook is swiveled by an increasing amount when it is pressed on this face. 
     In order to connect the airbag unit to the subassembly of the motor vehicle three snap-in hooks are preferably provided, plastic snap-in clips being associated with two snap-in hooks while an undercut in the opposite subassembly is associated with the third snap-in hook. However, is also possible that three snap-in hooks are provided for connecting the airbag unit to the subassembly of the motor vehicle, a plastic snap-in clip being associated with one snap-in hook while a respective undercut in the opposite subassembly is associated with the two further snap-in hooks. 
     The skeleton of the steering wheel is preferably provided as the subassembly of the motor vehicle to which the airbag unit is fastened. 
     In the case of an airbag unit arranged in a steering wheel, the airbag unit is movable in the direction of the steering wheel hub or of a contact bridge against the pressure of at least one spring in order to actuate at least one horn contact. 
     It is advantageous if the face of the swivelable section of the plastic snap-in clip associated with the snap-in hook has towards at least one side an oblique face such that the swivelable section can be pressed away from the snap-in hook by means of a pin in order to unlock the connection between the airbag unit and the subassembly of the motor vehicle. 
     Furthermore, it is also possible for the face of the snap-in hook associated with the swivelable section of the plastic snap-in clip to have towards at least one side an oblique face such that the swivelable section can be pressed away from the snap-in hook by means of a pin in order to unlock the connection between the airbag unit and the subassembly of the motor vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained with reference to exemplary embodiments and to drawings, in which: 
         FIG. 1  is a perspective view of a device according to the invention in a first embodiment; 
         FIG. 2  shows the snap-in operation of the inventive device; 
         FIG. 3  shows the snap-in position of the inventive device; 
         FIG. 4  is an isolated representation of a snap-in hook and a plastic snap-in clip; 
         FIG. 5  is a perspective view of the mounting of the plastic snap-in clip of the first embodiment; 
         FIG. 6  is a perspective representation of a bearing for a plastic snap-in clip in a second embodiment; 
         FIG. 7  shows a second embodiment of the plastic snap-in clip; 
         FIG. 8  is a perspective view of an inventive device with the second embodiment of the plastic snap-in clip; 
         FIG. 9  shows the snap-in operation of the embodiment according to  FIG. 8 ; 
         FIG. 10  shows the snap-in position of the embodiment according to  FIG. 8 ; 
         FIG. 11  shows the snap-in position of the embodiment according to  FIG. 8  with a horn contact; 
         FIG. 12  is a view in which the coordination of the snap-in hooks and the plastic snap-in clip can be seen; 
         FIG. 13  is a perspective view of a part of a steering wheel with bearings for the plastic snap-in clip of the second embodiment; 
         FIG. 14  is a perspective view of the underside of a snap-fastened device with a pin for unlocking; 
         FIG. 15  shows an embodiment in which the bearing for the plastic snap-in clip is mounted on a lateral wall; 
         FIG. 16  shows an embodiment in which one hook for a snap-in clip and two hooks for an undercut are provided. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a lower plate-shaped portion of an airbag unit  1  which is to be snap-fastened to a skeleton part  2 , for example a steering wheel hub or a contact bridge fastened to the steering wheel. For this purpose the airbag unit has on its underside snap-in hooks  3  with which plastic snap-in clips  4  on the skeleton part  2  are associated, which snap-in clips  4  have cylindrical projections  13  which are mounted pivotably in bearings  5  ( FIG. 2 ) on the skeleton part  2 . 
     It can be seen from  FIGS. 2 and 3  that the plastic snap-in clips  4  have a deformable section  6  and a swivelable section  7 . The plastic snap-in clips  4  are mounted in such a manner that the sections  6  and  7  project into an opening  8  of the skeleton part  2 . A side  10  of the deformable section  6  associated with a stop  9  of the opening  8  runs obliquely from the bearing  5  in the direction of the stop  9 . A side  11  of the swivelable section  7  associated with the snap-in hook  3  runs obliquely from the bearing  5  in the direction of the snap-in hook  3 . In order to snap-fasten the airbag unit  1  to the skeleton part  2 , the airbag  1  is pushed in the direction of the skeleton part  2 , as is indicated by the upper arrow in  FIG. 2 . As this is done, each snap-in hook  3  first comes into contact with the swivelable section  7  of one of the plastic snap-in clips  4 . As the snap-in hooks  3  continue to be pressed against the plastic snap-in clips, the deformable section  6 , the end of which rests against the wall of the opening  8 , is deformed in its region adjacent to the bearing, whereby the swivelable section  7  is swiveled in the direction of the deformable section  6 , as is represented by the curved arrow in  FIG. 2 . As this happens, the snap-in hook  3  engages in the opening  8 . As soon as the snap-in hook has passed the lower end of the swivelable section  7  the latter springs back, so that the snap-in position represented in  FIG. 3  is achieved. 
     In this position the left side of the snap-in hook  3 , in the illustration in  FIG. 3 , rests against the wall of the opening  8 . The hook is therefore prevented from sliding away to the side. When the airbag unit  1  is tensioned, for example during triggering of the airbag, the plastic snap-in clip  4  is only wedged further into the snap-in hook, since the swivelable section  7  disposed obliquely in the direction of the snap-in hook is pressed by the force acting on the underside  12  of said section  7  against the snap-in hook  3 . 
     One of the cylindrical projections  13  of the plastic snap-in clip  4  can be seen, in particular, in  FIG. 4 .  FIG. 5  shows the bearing  5  for the projections  13 . This bearing has two partially hollow-cylindrical bearings  14  spaced at a distance from one another. These bearings  14  are open at one side, so that the cylindrical projections  13  of the plastic snap-in clip can be pushed in. The plastic snap-in clip  4  is then located between the bearings  14 , as can be seen in  FIG. 5 . 
       FIG. 6  shows a bearing  5  for a second embodiment of the plastic snap-in clip. In this case the bearing  5  has a cylindrical bearing  15  between two brackets  16 . Associated with this bearing is a plastic snap-in clip  17  illustrated in  FIG. 7 , which has a partially hollow-cylindrical opening  18  which is open on one side in the manner of a claw. The plastic snap-in clip  17  has a deformable section  19  and a swivelable section  20 . 
       FIG. 8  shows a device with a variant  17   a  of this second embodiment of the plastic snap-in clip. In the case of this plastic snap-in clip  17   a , a swivelable section  20   a  is provided which has an upper wider region and the lower narrower region, so that a gap  20   b  is formed. An airbag unit  21  has two snap-in hooks  22  and a further snap-in hook  23 . Associated with each of the hooks  22  is one of the plastic snap-in clips  17   a , which are each mounted in one of the cylindrical bearings  15  which in turn are provided on a skeleton part  24 . In this case the deformable section  19  and the swivelable section  20   a  of each plastic snap-in clip  17   a  project into an opening  25  of the skeleton part  24 . An opening  26  which is partially covered by a part  27 , so that an undercut is formed, is associated with the snap-in hook  23 . 
     During installation of the airbag unit  21 , the hook  23  is first introduced into the opening  26  until the hook  23  engages under the part  27 . The airbag unit  21  is then moved with the hooks  22  in the direction of the swivelable sections  20   a , as is indicated by the arrow in  FIG. 9 . As it is pressed down further, each hook  22  engages in the associated opening  25  and swivels the section  20   a  in the direction of the deformable section  19  until the hook  22  engages in the gap  20   b , as shown in  FIG. 10 . In this position the airbag unit  21  is locked to the skeleton part  24 , the hooks  22  resting on one side against the respective plastic snap-in clip  17   a  and on the other against the lateral wall  25   a  of the respective opening  25 . In this embodiment, too, upon deployment of the airbag a self-blocking between the hook  22  and the plastic snap-in clip  17   a  is produced by the force F which is generated. 
       FIG. 11  shows an embodiment which is modified, as compared to the embodiment of  FIG. 10 , in that at least one horn contact  28 , with which an opposed contact  29  on the skeleton part  24  is associated, is provided on the airbag unit  21 . The distance between these two contacts is ensured by four springs  30 , which extend between nipples  31  on the airbag unit  21  and recesses  32  in the skeleton part  24 . One of these springs can be seen in  FIG. 11 . The position of the nipples  31  can be seen in  FIG. 12  and the position of the recesses  32  in  FIG. 13 . In the latter figure four opposed contacts  29  can also be seen, with which are associated four horn contacts  28 , only two of which are shown in  FIG. 12 . Self-evidently, a different number of horn contacts and corresponding opposed contacts may be provided. In this embodiment the hook  23  below the part  27  can be pressed downwards, whereby the airbag unit is swiveled about the bearings  15  and the horn contacts  28  are pressed against the opposed contacts  29 . 
       FIG. 14  shows the underside of the airbag unit  21  and of the skeleton part  24  in the position in which they are connected to one another. The undersides of the snap-in hooks  22 ,  23  and of the swivelable sections  20   a  of the plastic snap-in clips  17   a  can be seen. 
     The face of the snap-in hook  22  associated with the respective swivelable sections  20   a  of the plastic snap-in clips  17   a  has an oblique face  33  such that each swivelable section  20   a  can be pushed away from the respective snap-in hook  22  by means of a pin  34  in order to unlock the connection between the airbag unit  21  and the skeleton part  24 . In the embodiment of  FIG. 14 , the swivelable sections  20   a  additionally have oblique faces  35 ,  36 , whereby unlocking is further facilitated. For guidance of the pin  34 , a lateral channel  37  is provided on the underside of the skeleton part  24  in the region of each swivelable section  20   a.    
     In the embodiment of  FIG. 15 , a skeleton part  38  with lateral walls  39  is provided in place of a plate-shaped skeleton part. In this embodiment the cylindrical bearings  15  are mounted on the lateral walls  39 .  FIG. 15  shows a bearing with a plastic snap-in clip  17   a . Associated with the latter is a snap-in hook  40  on an airbag unit  41 . After latching, the airbag unit  41  is located between the lateral walls  39 , so that the airbag unit is securely locked. The opposite lateral wall  39  is not shown in  FIG. 15 . 
       FIG. 16  shows an embodiment in which one snap-in hook  22   a  is associated with a plastic snap-in clip (not shown) and two snap-in hooks  23   a  are associated with respective undercuts (not shown). The plastic snap-in clip corresponds to the plastic snap-in clips shown in  FIG. 12 , and the undercuts correspond to the undercut shown in  FIG. 12 , which is formed by an opening  26  and a part  27 .