Abstract:
An airbag module is mounted on a steering wheel in such a way that its vibrations are damped. It is connected to the steering wheel by at least one elastic element which has an isolated area for attaching a fixing element of the module.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a steering wheel with an airbag module. 
     2. Description of the Related Art 
     In motor vehicle steering wheels the rigid coupling to the steering column gives rise to the problem of vibrations occurring in the steering wheel, at least in certain speed ranges. These vibrations are caused by the natural frequency of the airbag-steering wheel as a function of a certain engine speed. In addition to shifting the natural frequency of the airbag-steering wheel to a frequency range lying outside the range of the oscillations actually occurring on the steering wheel by fitting an additional mass to the steering wheel, DE 37 10 173 A1, for example, discloses an arrangement wherein, in order to reduce the vibrations, a airbag unit is mounted via a vibration-damping housing to the steering wheel in such a way that it is relatively moveable transversely to the longitudinal axis of the steering column in relation to the steering wheel. 
     In addition, it is proposed that the housing also be moveable in the direction of the longitudinal axis of the steering column. This mobility is achieved in that retaining clips are arranged at the sides of the housing. These have bearing bushes possessing sound-damping characteristics which are disposed in corresponding holes. The bearing bushes guide lock screws for fixing the retaining clips to the spokes of the steering wheel. There is a clearance between the shank of each lock screw and the respective bush, which permits lateral displacement of the retaining clips in relation to the lock screws. 
     A floating bearing is therefore obtained. In this case the entire airbag module the cap, which screens it off from the compartment, is mounted on a floating bearing. 
     The disadvantage of this arrangement is that it is relatively expensive. 
     SUMMARY OF THE INVENTION 
     The object of the invention, therefore, is to obtain a vibration-damped mounting of the airbag in the steering wheel at lower cost. 
     According to the invention, this is achieved by a steering wheel having airbag module which is supported on the steering wheel by a vibration-damped mounting. In this arrangement the airbag module is connected to the steering wheel by at least one elastic element, which has an isolated area for fixing a retaining element of the airbag module. In particular the elastic element has a bush-shaped first section for fixing to the steering wheel and a bush-shaped second section with isolated area for the fixing of the airbag module, the second section surrounding the first section with clearance and being connected to the first section at one side. 
     Such an elastic element is easy to manufacture, assemble and connect to the airbag module. The elastic element can thus be connected directly to the steering wheel. In a preferred embodiment, however, the first section is fixed on a rigid bush, which can in turn be connected to the steering wheel by a bolt and nut. 
     It is advisable for the elastic element to be connected to the airbag module at the isolated end of the second section, since in this case maximum damping is achieved. It is furthermore advisable for the elastic element to be composed of an elastomer. 
     The elastic element is preferably molded on to a carrier plate for a gas generator. 
     The internal and external contour of the bush-shaped first and second sections preferably have a circular cross section. 
     In a further development it is proposed that the first section has an irregular wall thickness, its internal and external contours lying eccentrically to one another, for example. In this way a directional oscillation behavior is achieved. 
     In a further embodiment it is proposed to design the first bush-shaped section with a taper, the cross section diminishing from the point of connection to the second section onwards, for example. 
     Furthermore, the second bush-shaped section may also taper, the cross section increasing from the point of connection to the first section onwards, for example. 
     In a preferred embodiment four elastic retaining elements are provided on a carrier plate for the gas generator. 
     In a further development it is proposed that the airbag module and a cap for covering it be fixed to the steering wheel separately from one another, the cap being firmly connected to the steering wheel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained through examples of embodiments, with reference to drawings, in which: 
     FIG. 1 shows a section through a steering wheel airbag module, which is arranged on an element; 
     FIG. 2 shows an enlarged representation of the element represented in FIG. 1; 
     FIG. 3 shows a top view of a carrier plate generator with four elastic elements; and 
     FIG. 4 shows a section through FIG. 3 along 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A steering wheel  1  has a steering wheel skeleton  2 , which is covered by polyurethane foam  3 . An airbag module  4  is arranged inside the steering wheel  1 . The module has a gas generator  5 , an airbag retaining plate  6 , an airbag  7  and a fold space restrictor plate  8  with a cover  9 . These components of the airbag module are fixed by means of screws  10  to a carrier plate  11 , which is supported In three elastic elements  12 , only one of which is visible in FIG.  1  and which act as isolating elements. By way of connecting plates  13 , these elements are connected by means of screws  15  to a moving contact  22 , which is in turn connected by means of screws  23  to the steering wheel skeleton  2 . The elastic elements  12  are fixed to the connecting plates  13  by means of bolts  14  and nuts  16 . 
     Due to the provision of the elastic elements  12 , few if any vibrations of the steering wheel are transmitted to the airbag module. 
     A cap  17 , which covers the airbag module  4  off from the passenger compartment, is connected to the steering wheel skeleton  2  by the connecting plates  13 . The connection between the cap  17  and the connecting plates  13  is achieved in that the latter are bent over in a hook shape at their upper end  18  and are snapped by the upper end into openings  19  in a side wall  21  of the cap  17 . The cap is thus connected to the steering wheel skeleton  2  without any oscillating elements, and when vibrations occur it oscillates in approximately the same way as the steering wheel. This means that there is scarcely any relative movement between the cap  17  and the surface of the steering wheel, so that a slot  20  between the cap  17  and the steering wheel  1  can be small, thereby improving the appearance of the steering wheel. 
     This mounting according to the invention can be used both for an airbag module that is fixed to the steering wheel and for an airbag module that is displaceable in relation to the steering wheel skeleton for operating the horn (floating horn), as is shown in FIG.  1 . In that figure the moving contact  22  with an electrical contact  24  is displaceable in the direction of the steering wheel skeleton  2  having an opposing electrical contact  25 . Displacement of the moving contact  22  is possible in that it has bushes  26  in the area of the screws  23 , the bushes being displaceable on the screws  23  against the pressure of a spring  27 . In response to pressure on the cap  17 , the moving contact  22  is therefore displaced together with the airbag module  4 , until the contact  24  and the opposing contact  25  touch one another, thereby operating the horn. 
     FIG. 2 shows an enlargement of the elastic element  12  used in FIG.  1 . This element has a rigid bush  28 , which has a flange-like edge  29  at the bottom. Extending around the bush is a first bush-shaped section  30  of elastic material, which is surrounded with clearance by a second bush-shaped section  31  of elastic material. The two sections are connected to one another in the area of the edge  29 , thereby constituting a single part in this example of an embodiment. The bush  28  and also the sections  30 ,  31  have a circular cross section. 
     The first bush-shaped section  30  tapers from the point of connection to the second section  31  onwards, the cross section diminishing upwards. Furthermore the internal contour  32  and the external contour  33  of the first section  30  lie eccentrically to one another, so that this section has an irregular wall thickness. 
     The second bush-shaped section  31  also tapers from the point of connection to the first section onwards, the cross section increasing upwards. The upper end  34  of this section is connected as isolated area to the carrier plate  11 . 
     The isolated area is particularly suitable for damping both radial and axial oscillations and thereby also for correspondingly damping the oscillation of the carrier plate  11 . Furthermore, this elastic element  12  is easy and inexpensive to manufacture and assemble and takes up little space. 
     FIG. 3 shows a carrier plate  35 , in which four elastic elements  36  are provided. The carrier plate  35  is double-bent in the area of the elastic elements, as can be seen in particular from FIG.  4 . 
     The carrier plate  35  has holes  37  to receive a gas generator (not shown). The elastic elements  36  have a bush-shaped first section  38  and a bush-shaped second section  39 , which are cylindrical and coaxial with one another. As in the preceding example of an embodiment, the first section is fixed on a rigid bush  28 . The second section is provided with a widened edge  40  at the top to receive the carrier plate  35 .