Abstract:
The invention relates to an assembly unit comprising an airbag module, a vehicle steering wheel, horn contacts and attachment devices by means of which the airbag module is attached to the steering wheel. A first detachable attachment device is provided which comprises a first holding part provided on the airbag module and a second holding part provided on the steering wheel. The holding parts engage with each other and allow a swiveling of the module in a direction towards the steering wheel in order to close a second attachment device. The second attachment device is a detachable latching connection and the airbag module, in its attached state, is able to be moved axially in order to close said horn contacts.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to an assembly unit comprising an airbag module, a vehicle steering wheel and attachment means with which the airbag module is attached to the steering wheel.  
         BACKGROUND OF THE INVENTION  
         [0002]    To put it more precisely, the invention relates to a so-called airbag module in the form of a “floating horn module”, i.e. an airbag module that is attached to the vehicle steering wheel in such a way that it can be moved axially in order to close two horn contacts by pressing on the airbag module.  
           [0003]    Usually, airbag modules are attached to a horn plate by means of at least two laterally arranged attachment screws. During the assembly process at the automobile manufacturer, in order to ensure that the module is centered on the steering wheel, a first screw has to be tightened slightly and, after the steering wheel has been turned, the second screw likewise has to be tightened. Finally, after the steering wheel has been turned once again, the first screw is tightened completely. This assembly method is time-consuming and expensive. For this reason, snap connections were developed in the form of several hooks provided on the rear of the module, the hooks extending into the horn plate or directly into the skeleton. This makes it possible to clip the module onto the horn plate or onto the steering wheel. Thus, the assembly is less time-consuming, although the disassembly, in which the hooks are grasped by a special tool and bent into a release position, is often difficult.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    Therefore, the object of the invention is to achieve a fast assembly as well as a fast disassembly of the assembly unit. This is achieved with an assembly unit comprising an airbag module, a vehicle steering wheel, horn contacts and attachment devices by means of which the airbag module is attached to the steering wheel. The attachment devices comprise at least one first and one second detachable attachment device. A first detachable attachment device has a first holding part provided on the airbag module and a second holding part provided on the steering wheel. The holding parts engage with each other and allow a swiveling of the module in a direction towards the steering wheel in order to close the second attachment device. The second attachment device is a detachable latching connection. The airbag module, in its attached state, is able to be moved axially in order to close the horn contacts.  
           [0005]    With the assembly unit according to the invention, numerous snap connections are replaced by providing the first attachment means. Therefore, for the disassembly, far fewer tools have to be inserted laterally between the module and the steering wheel in order to bend the latching hooks into a release position that allows the module to be lifted off the steering wheel. The first attachment means is very simply designed, for it includes only the first and second holding parts, in other words, no screws or the like are provided to connect the first holding part and the second holding part to each other. The disassembly of the holding parts is also correspondingly simple. Preferably, the two holding parts are only connected to each other by being slid into each other, i.e. they are configured in such a way that the module is placed on the side of the first attachment means at a slight tilt toward the steering wheel and then, when the two holding parts are next to each other, the module has to be shifted until the two holding parts engage with each other. Subsequently, the upward tilted end of the module can be swiveled toward the steering wheel until the latching connection closes. The disassembly can simply be done in the reverse direction. The latching connection is detached, the module is tilted upward and shifted slightly laterally or radially until the holding parts are no longer engaged with each other.  
           [0006]    In this manner, with the assembly unit according to the invention, only one latching connection is necessary to lock the airbag module in place. Preferably, in fact, just one attachment means can be provided.  
           [0007]    Preferably, it is provided that the first and/or the second attachment means is/are configured in such a way that, when the module is in the arrested state, it/they permit/s the module to be moved axially in order to close the horn contacts. Concerning the first attachment means this means is a swivel bearing as well as an axial guide. According to this embodiment, the module is attached to the steering wheel itself or to a part that is affixed to the steering wheel. In this first embodiment, it can be provided that a return element, that is close to the first attachment means and that is provided so as to stabilize the position of the holding parts, simultaneously constitutes the return element that serves to force the module back into the initial position after the horn has been actuated.  
           [0008]    A second embodiment makes provision that the airbag module is not attached directly to the steering wheel skeleton as in the first embodiment, but rather to a horn plate on which the module is locked via the attachment means. In order to actuate the horn, the horn plate can be moved axially relative to the steering wheel skeleton, so that the horn plate, together with the module, is pushed by the driver toward the skeleton. In this embodiment, the horn plate as defined in the main claim is to be associated with the vehicle steering wheel. In this embodiment, however, the elastic return elements for forcing the module back into the initial position, on the one hand, and the elements for stabilizing the position of the holding parts in the locked position, on the other hand, are distinct elements.  
           [0009]    It is advantageous if the return element is situated near the first attachment means in such a way that it pushes the holding parts into a locked position. This prevents the holding parts from being moved with respect to each other into an unlocking position, so that the return element has a double function.  
           [0010]    Moreover, the second attachment means can also be associated with an elastic return element.  
           [0011]    In the preferred embodiment, the first and the second attachment means are provided on opposite outer edges of the module in order to increase the stability of the module. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a cross-section through an assembly unit according to the invention of a first embodiment and,  
         [0013]    [0013]FIG. 2 is a cross-section through an assembly unit according to the invention of a second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    [0014]FIG. 1 shows a first embodiment of an assembly unit, consisting of an airbag module  10 , a steering wheel and attachment means with which the airbag module  10  is attached to the steering wheel. The steering wheel itself is made up of a steering wheel skeleton  12 , a metal plate  14  screwed onto it and a horn plate  16  that is movably mounted axially to the metal plate  14  by means of several pins  18 , only one of which is shown here. There is an elastic return element  20  around each pin  18 . The horn plate  16  and the metal plate  14  have horn contacts  22  that are at a distance from each other when the horn is not in the actuated position. When the horn plate  16  is pressed downwards, the elastic return elements  20  yield until the horn contacts  22  are closed, that is to say, until they touch each other. After the horn has been actuated, the elastic return elements  20  force the horn plate back up into the initial position shown.  
         [0015]    The airbag module  10  comprises a pot-shaped receptacle  24  in which an airbag  26  and a gas generator  28  are accommodated and also comprises a baseplate  30  that serves to close the receptacle  24 . The airbag module is attached merely via two attachment means  32 ,  34  to the horn plate  16 . The first attachment means has a first holding part  36  that is affixed to the edge of the baseplate  30  and that is in the form of a hook-shaped end facing radially outwards, namely, in the form of an L-shaped end  38 . On the steering wheel, namely, on the horn plate, there is a second holding part  40  in the form of a stirrup with a rectangular receiving opening. The free end  38  of the first holding part  36  has been slid through the receiving opening of the stirrup  40  in such a way that the holding parts  36 ,  40  engage each other in the position shown. In order to prevent lateral shifting of the holding parts  36 ,  40  that form the first attachment means  32 , the free end  38  is covered with a covering  42  made of an elastomer. Furthermore, the covering  42  prevents rattling noises. One or more ribs  44  on the holding part  36  form a lateral stop so that the second holding part  40  is clamped laterally between the elastic covering  42  and the rib or ribs  44 .  
         [0016]    So that the module  10  does not slip downwards in the area of the first attachment means  32 , so that the module  10  is pre-stressed in an axial, upward direction and so that the holding parts  36 ,  40  do not become disengaged, there is an elastic return element  46  situated between the baseplate  30  and the horn plate  16 , near the first attachment means  32 . The elastic return element  46  strives to keep the holding parts  36 ,  40  in the position shown and to push the module  10  upwards.  
         [0017]    On the edge of the airbag module opposite from the first attachment means  32 , there is arranged a second attachment means  34  that consists only of one latching connection. A latching hook  48  projects from the back of the baseplate  30  and, in the locked position, the latching hook  48  extends through an opening  50  in the horn plate  16  and grasps behind the horn plate  16 . An elastic stirrup spring  52 , preferably in the form of a leg spring, secures the latching connection. In addition or as an alternative, an element corresponding to the return element  46  can be provided in the area of the second attachment means  34 . The latching hook  48  is surrounded by a helical spring  53  that serves to return the module and to stabilize the position of the latching connection.  
         [0018]    The airbag module  10  is attached to the horn plate  16  in that the edge of the module  10  is moved near the first holding part  36  in a more or less tilted position downward to the horn plate  16  and is then shifted laterally until the first holding part  36  engages with the second holding part  40 . In this state, the two holding parts  36 ,  40  allow a downward swiveling of the edge of the module close to the latching hook  48 . The latching hook  48  finally latches with the stirrup spring  52 . During the assembly, the return elements  46  and the stirrup spring  52  have to be slightly pressed together. After the module  10  is released, however, they push the module back upwards again so that the module  10  is locked firmly to the horn plate  16  by means of just two attachment means  32 ,  24 . The elastic return elements  46  are preferably elastomers that also prevent a lateral shifting of the module  10  towards the horn plate  16 , while also preventing rattling noises.  
         [0019]    Theoretically, the assembly could also be carried out without a swiveling of the module  10 . For this purpose, the module  10  could be placed from the top on the horn plate  16 , with reference to FIG. 1 offset to the right, and subsequently moved downwards under axial pressure so far to the left until the latching connection is engaged. After the module is released, the return elements  46  would bring the module into the position shown.  
         [0020]    However, if the holding parts  36 ,  40  first engage with each other in order to form a swivel bearing, then the latching hook  48  is reliably guided into the opening  50  so that this opening, unlike in the second assembly version, does not first have to be “sought”. In order to form a non-tilting swivel bearing, it can be necessary for the first attachment means  32  to be made up of two consecutively arranged holding parts  36 ,  38  or else of additional such pairs, in order to diminish the risk of tilting for the module  10 .  
         [0021]    Since the two attachment means  32 ,  24  can be non-destructively detached and since only one latching connection is provided, the module  10  can be disassembled very quickly in that, from below the horn plate  16 , a tool is inserted radially inwards in order to press the stirrup spring  52  to the right into a release position. The module  10  is detached from the horn plate  16  upwards and with a swiveling motion.  
         [0022]    The embodiment according to FIG. 2 is very similar to that of FIG. 1, so that only the differences need to be elaborated upon.  
         [0023]    In this embodiment, the horn plate  16  is rigidly attached to the skeleton  12  or to the metal plate  14 . Therefore, the horn plate  16  is not moved along when the horn is actuated, that is to say, when the module  10  is pressed downwards. Consequently, an axial movement is only possible between the module  10  and the horn plate  16 . Since the first attachment means  32  is configured here as a pure swivel bearing, the module  10  can only be pressed downwards in the area of the second attachment means  34  in order to close the horn contacts  22 . This is why, in the area of the second attachment means  34 , the horn contacts  22  are provided on the top of the horn plate  16 , on the one hand, and on the rear of the baseplate  30 , on the other hand.  
         [0024]    The two attachment means  32 ,  34  not only allow the easy assembly and disassembly already described in conjunction with FIG. 1, but they also allow a movement (swiveling) of the airbag module  10  towards the horn plate  16  until the horn contacts  22  are closed. The return element  20  of FIG. 1 can be dispensed with. Its function is performed by the elastic return elements  46  and optionally additionally by the spring element  53 .  
         [0025]    As an alternative to the embodiment shown in FIG. 2, the metal plate  14  and the horn plate  16  can be left out so that the module is attached directly to the skeleton  12 . For this purpose, the skeleton  12  has the second holding part  40  as well as the opening  50 .