Abstract:
A device for triggering an airbag device that is accommodated in a steering wheel is described. The device has a firing cap for an airbag device that is accommodated in a steering wheel and is fired by a light pulse that is supplied via an optical waveguide. A coupling device, which decouples the optical waveguide from the rotation of the steering wheel but ensures that the light pulse is transmitted into the firing cap from the optical waveguide and also ensures that the airbag is inflated by a gas generator, is provided between the optical waveguide and the airbag.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of copending International Application PCT/DE00/02777, filed Aug. 16, 2000, which designated the United States. 
     
    
     
       BACKGROUND OF THE INVENTION  
       FIELD OF THE INVENTION  
         [0002]    The invention relates to a device for triggering an airbag device accommodated in a steering wheel. The device contains a gas generator for inflating an airbag, a firing cap for firing the gas generator and an optical waveguide that is connected to a light source remote form the steering wheel and has the purpose of supplying the firing cap with a light pulse which fires the firing cap.  
           [0003]    A device of the generic type is known from the German Patent DE 196 33 409 C1. The optical waveguide, for example a glass fiber, is optically connected to the firing cap in such a way that the firing cap is directly fired by light pulses with a sufficient energy content, whereas light pulses with a smaller energy content are used as test pulses which can be reflected using suitable devices and used to check the optical waveguide. The aforesaid patent does not contain any details on the connection of the optical waveguide to the firing cap. This connection is generally of rigid construction, which leads to increased constructional complexity in an airbag device which is accommodated in a steering wheel and rotates with the steering wheel because such optical waveguides can in themselves only be twisted to a small degree.  
         SUMMARY OF THE INVENTION  
         [0004]    It is accordingly an object of the invention to provide a device for triggering an airbag device that is accommodated in a steering wheel which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has a simple structure with a high degree of functional reliability.  
           [0005]    With the foregoing and other objects in view there is provided, in accordance with the invention, a device for triggering an airbag device accommodated in a steering wheel assembly having a steering wheel. The device contains a gas generator for inflating an airbag, a firing cap for firing the gas generator, a light source, and a coupling device having an optical waveguide connected to the light source remote from the steering wheel. The light source supplies the firing cap with a light pulse for firing the firing cap. The coupling device is disposed at least approximately concentrically with respect to an axis of rotation of the steering wheel. The coupling device is disposed between the airbag and the light source, and the coupling device configured such that the optical waveguide is isolated from a rotation of the steering wheel and ensures a functional connection of the optical waveguide to the firing cap.  
           [0006]    According to the invention, the optical waveguide via which the light pulses for firing the firing cap are fed in from a light source is decoupled from the steering wheel in terms of rotation of the steering wheel so that the optical waveguide is not torsionally loaded. The coupling device, via which the rotational decoupling and the functional coupling are effected in the transmission path from the optical waveguide via the firing cap to the gas generator and from there to the airbag, is disposed concentrically or coaxially with respect to the axis of rotation of the steering wheel so that the function is ensured irrespective of the rotary position of the steering wheel.  
           [0007]    In accordance with an added feature of the invention, the optical waveguide is a two-piece waveguide with an end part to be fixed to the steering wheel and ends at the firing cap, and a feed part starting from the light source. The feed part is isolated from the steering wheel in terms of its rotatability. The feed part has a first light exit window and the end part has a second light entry window disposed opposite the first light exit window of the feed part coaxially with the axis of rotation of the steering wheel.  
           [0008]    In accordance with an additional feature of the invention, the decoupling device includes a bearing to be attached to a steering column of the steering wheel. The feed part has a steering-wheel end accommodated in the bearing and the steering column is connected fixed in terms of rotation to the steering wheel.  
           [0009]    In accordance with another feature of the invention, the gas generator is to be connected fixed in terms of rotation to the steering wheel and is rotatable in relation to the firing cap, and the firing cap is provided coaxially to the axis of rotation of the steering wheel and is decoupled from the steering wheel in terms of rotation.  
           [0010]    In accordance with a further feature of the invention, the gas generator has a recess formed therein and the firing cap is accommodated in the recess. The decoupling device has a bearing disposed between the gas generator and the firing cap.  
           [0011]    In accordance with another added feature of the invention, the firing cap is connected fixed in terms of rotation to the steering wheel and is rotatable in relation to an end of the optical waveguide facing the firing cap.  
           [0012]    In accordance with another additional feature of the invention, the firing cap has a housing with a through-opening formed therein, and the optical waveguide is accommodated in the through-opening in the housing of the firing cap. The decoupling device has a bearing disposed in the housing and the optical waveguide has an end part accommodated in the bearing.  
           [0013]    In accordance with another further feature of the invention, the end part of the optical waveguide has a light exit window, and a fluorescent film is disposed between the light exit window of the optical waveguide and the firing cap.  
           [0014]    In accordance with a concomitant feature of the invention, the steering wheel assembly has a steering column connected fixed in terms of rotation to the steering wheel. The decoupling device has a bridging tube to be disposed in the steering column and rigidly connected to a wall of the steering wheel assembly. The optical waveguide is guided from an exterior space through the bridging tube into an interior of the steering column. The decoupling device has a bearing disposed between the bridging tube and the steering column.  
           [0015]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0016]    Although the invention is illustrated and described herein as embodied in a device for triggering an airbag device which is accommodated in a steering wheel, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0017]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will he best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a diagrammatic, sectional view of a first embodiment of an airbag device that is fixed to a steering wheel and is triggered by a light pulse according to the invention;  
         [0019]    [0019]FIG. 2 is a detailed, sectional view of a further embodiment of the airbag device;  
         [0020]    [0020]FIG. 3 is a detailed sectional view of a modified embodiment of the airbag device; and  
         [0021]    [0021]FIG. 4 is a detailed sectional view for explaining how an optical waveguide is led through to a steering spindle. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown an airbag device which is designated in its entirety by reference numeral  4  and is accommodated in a steering wheel which is illustrated in an approximate form and designated by reference numeral  2 .  
         [0023]    The airbag device  4  includes an airbag  6  (illustrated in its folded-up position) that is attached to a gas generator  8  that is rigidly connected to the steering wheel  2 . The gas generator  8  has a recess  10  that accommodates a housing  12  of a firing cap that is designated in its entirety by  14 .  
         [0024]    The housing  12  is closed off from the gas generator  8  by a plate  16 . A highly flammable firing powder  17  is accommodated in the interior of the housing  12 .  
         [0025]    The housing  12  has a through-opening which is directed downward according to FIG. 1 and in which an end part  18  of an optical waveguide is attached, for example by bonding. A light exit window  20  of the end part  18  directly adjoins the firing powder  17  or a fluorescent film  22  that is disposed on a floor of the housing  12 .  
         [0026]    A light exit window  26  of a feed part  28  of the optical waveguide is disposed opposite the light entry window  24  of the end part  18 , the optical waveguide being divided in two and being connected to a light source  30  which is embodied, for example, as a laser diode and is actuated by a control unit  32 . A free end region of the feed part  28  is secured in a sliding bearing  34  that is accommodated between two securing bushings  36 , which are inserted into a steering column  38  that is connected fixed in terms of rotation to the steering wheel  2 .  
         [0027]    The entire configuration is such that the light entry window  24 , which rotates along with the steering wheel  2 , of the end part  18  is aligned concentrically with respect to the axis A-A of rotation of the steering wheel  2  and of the steering column  38 , respectively. The light exit window  26  of the feed part  28  is located opposite the light entry window  24  and at a short distance from it. The light exit window  26  is also aligned concentrically with respect to the axis A-A of rotation so that when the steering wheel  2  rotates, the alignment of the two windows  24  and  26  with respect to one another is maintained, while the feed part  28  does not rotate owing to its positioning within the steering column  38 . It goes without saying that the entire firing cap  14 , with the end part  18 , are advantageously aligned concentrically with respect to the axis A-A of rotation. The concentric alignment of the windows  24  and  26  does not have to be completely precise; it is sufficient if a significant overlap is maintained during rotation.  
         [0028]    The function of the airbag device  4  and the firing of the firing cap  14  by a light pulse which is output by the light source  30  and the generation of gas in order to inflate the airbag  6  in the gas generator  8  after its activation by firing the firing cap  14  and exploding the plate  16  are known per se and are therefore not explained. The configuration of the windows  24  and  26  at a small mutual distance and coaxially with respect to the axis A-A of rotation constitutes a coupling device which is used to decouple the feed part  28  of the optical waveguide from the rotation of the steering wheel  2 , but the optical and functional coupling between the feed part  28  and the end part  18  or firing cap  14  is ensured. It goes without saying that the gap between the two windows  24  and  26  is small so that the transmission of the light pulse from the feed part  28  into the end part  18  takes place without significant optical losses. The function of the fluorescent film  22  is that when there is directional use of the optical waveguide for diagnostic purposes, the fluorescent film is excited by weak test pulses and light is irradiated back into the optical waveguide.  
         [0029]    [0029]FIG. 2 shows a modified embodiment of a coupling device, the same reference symbols as in FIG. 1 being used for functionally identical components.  
         [0030]    In contrast to the embodiment according to FIG. 1, in the embodiment according to FIG. 2 the firing cap  14  is mounted concentrically with respect to the axis A-A of rotation of the steering wheel  2  in the gas generator  8  so as to be capable of rotating with the aid of a sliding bushing  50  which is inserted into the recess  10  of the gas generator  8 . In order to protect the sliding bushing  50 , an attachment bushing or screw bushing  52  is screwed into the gas generator  8 .  
         [0031]    Because the firing cap  14  in the embodiment according to FIG. 2 is decoupled in terms of rotation from the gas generator  8  that is rigidly connected to the steering wheel  2 , the optical waveguide  54  can be embodied in one part and rigidly connected to the firing cap  14  or to the housing  12 .  
         [0032]    When the firing cap  14  is fired using a light pulse that is fed by the optical waveguide  54 , energy that is released owing to the ignition of the firing powder is conducted into the gas generator  8  where it triggers the generation of gas, which inflates the airbag  6 . The decoupling in terms of rotation but functional coupling between the optical waveguide  54  and the gas generator  8  or the airbag  6  is achieved in the embodiment according to FIG. 2 by the positioning of the firing cap  14  in the gas generator  8 .  
         [0033]    [0033]FIG. 3 shows an embodiment which is modified with respect to FIG. 1 in a different way to that of FIG. 2. In the embodiment according to FIG. 3, the firing cap  14  is in turn rigidly connected to the gas generator  8  that is rigidly connected to the steering wheel  2 . The end of the optical waveguide  54  is accommodated in a sliding bushing  60  that is inserted into a through-hole  62  in the base wall of the housing  12  of the firing cap  14 . In order to secure the sliding bushing  60 , a screw bushing  64  is provided. A light exit window  66  of the optical waveguide  54  is located directly underneath the fluorescent film  22 , which is inserted into the base region of the firing cap  14 . The decoupling in terms of rotation between the rotation of the steering wheel  2  and of the steering column  38  and the optical waveguide  54  takes place as a result of its positioning in the through-hole  62 . The functional coupling is affected directly underneath the fluorescent film  22  by the configuration of the light exit window  66 . Of course, the configuration is again advantageously effected such that there is concentricity with the axis A-A of rotation.  
         [0034]    [0034]FIG. 4 shows an exemplary embodiment indicating how the optical waveguide  54  is introduced into the interior of the steering column  38  or of a steering spindle  68  that is disposed at the end of the steering column  38 . The steering spindle  68 , which operates in a steering gear known per se, whose interior is filled with hydraulic fluid  40  or steering oil, has a through-duct  70 . A bridging tube  74 , which is led through a wall  78  of the steering gear while being sealed by a sealing ring  76  is inserted into a step-shaped widening at the end of the through-duct  70  with intermediate configuration of a radial shaft sealing ring  72 . In this way, the through-duct  70  of the steering spindle  68  passes on toward the outside through the bridging tube  74 , which is decoupled in terms of rotation from the steering wheel  2  using the radial shaft sealing ring  72 , so that the optical waveguide  54  can be introduced. The seals  72  and  76  enable the through-duct  70  or the interior of the junction tube  74  to be separated in a sealed fashion from the interior of the fluid-filled steering gear.  
         [0035]    Of course, the invention can be used and modified in various ways. For example, the steering spindle  68  in FIG. 4 does not have to interact in a direct mechanical fashion with the actual steering gear or a steering tie rod. The steering spindle  68  or the steering column  38  (FIG. 1) can also be the steering sensor of a steering system in which the steering gear which actuates the steering tie rods is controlled via hydraulic lines or electrical lines. The decoupling in terms of rotation between the steering wheel  2  and the optical waveguide can also be effected in such a way that the entire airbag device is decoupled in terms of rotation from the steering wheel  2  or only the airbag  6  is attached fixed in terms of rotation to the steering wheel  2  and can rotate in relation to the gas generator  8 . The fluorescent film  22  is not necessarily a component of the configuration. The firing powder or the firing material can be fired directly by the light pulse that emerges from the directly adjoining light exit window of the optical waveguide.