Abstract:
A steering wheel assembly has a steering wheel and an airbag disposed about the steering wheel. The airbag is contained within an airbag housing spaced from an airbag inflator to form a gap between the airbag inflator and the airbag housing. A shield selectively bridges the gap between the airbag inflator and the airbag housing.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a damper for a steering wheel assembly.  
         BACKGROUND OF THE INVENTION  
         [0002]    Most steering wheels require a mass damper to dampen the vibration of a steering wheel, which may vibrate as a consequence of road conditions. The mass damper serves to reduce or eliminate vibration of the steering wheel for an anticipated range of frequencies. A mass damper, however, is expensive and requires space inside the limited room offered by a steering wheel assembly. Moreover, the mass damper increases the total mass of the steering wheel.  
           [0003]    Driver side airbag modules are located in the limited space offered by the steering wheel assembly. The airbag module may comprise an airbag, airbag housing, and airbag inflator as a single unit installed within the steering wheel assembly. It has been suggested to use the airbag inflator as the mass damper for the steering wheel. However, the use of the airbag inflator as a damper presents challenges. One such challenge is preventing the leakage of gas from the inflator into the passenger compartment during deployment of the airbag. This gas is typically hot, and it would be undesirable to release the gas into this compartment.  
           [0004]    There is therefore a need to use the airbag inflator as a mass damper while still preventing the leakage of gas from the airbag housing into the passenger compartment.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention comprises a steering wheel assembly that uses an airbag inflator as a mass damper. An airbag is stored in an airbag housing. The housing is spaced from the airbag inflator to permit the free movement of the inflator relative to the steering wheel, thereby permitting the inflator to act as a mass damper. As a consequence of this spacing, a gap between the airbag inflator and the airbag housing exists. Upon activating of the airbag inflator, a shield bridges the gap between the airbag inflator and the airbag housing, directing the gas from the inflator to the airbag and preventing the gas&#39; escape into the passenger compartment.  
           [0006]    The shield may deform from the pressure of the escaping gas from the airbag inflator and, by deforming, bridge the gap between the airbag inflator and the airbag housing. The shield may comprise a ring having overlapping segments to promote deformation. In addition, the shield may comprise two layers with one layer folded over a portion of the other layer to provide additional protection against the escape of gas.  
           [0007]    In this way, the shield may serve to seal a gap between the airbag housing and the airbag inflator. Thus, during normal operation of the vehicle, the shield is drawn away from the gap to permit the free movement of the airbag inflator. Upon activation of the airbag inflator, the shield closes the gap. Accordingly, the airbag inflator may be supported to move freely relative to the steering wheel and thus damp its vibration by a resilient connection to the steering wheel. The airbag inflator may be tuned to damp a range of vibration frequencies of the steering wheel so as to limit steering wheel vibration.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.  
         [0009]    [0009]FIG. 1 illustrates the inventive steering wheel assembly, including airbag inflator, airbag housing, and shield.  
         [0010]    [0010]FIG. 2 illustrates a close up view of the invention of FIG. 1 highlighting a gap between airbag housing and airbag inflator.  
         [0011]    [0011]FIG. 3 illustrates a bridging of the gap of FIG. 2 during deployment of an airbag.  
         [0012]    [0012]FIG. 4 illustrates an alternative placement of a shield.  
         [0013]    [0013]FIG. 5 illustrates an alternative mounting feature of the invention.  
         [0014]    [0014]FIG. 6 illustrates a double folded shield.  
         [0015]    [0015]FIG. 6A illustrates a double folded shield in its actuated position.  
         [0016]    [0016]FIG. 7 illustrates a segmented ring shield.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 illustrates the inventive steering wheel assembly  10 . The steering wheel assembly  10  comprises a steering wheel  14 , shown in cross-section, in which is disposed an airbag  18 , an airbag housing  22  and an airbag inflator  26 . The steering wheel  14  is connected to the steering column  15  through a bolt  16 . In prior airbag designs the airbag, airbag housing, and airbag inflator form a single unit.  
         [0018]    To permit the use of an airbag inflator  26  as a vibration damper, the airbag inflator  26  is separated from an airbag housing  22  thereby creating a gap  30  between the airbag inflator  26  and the airbag housing  22 . In this way, the airbag inflator  26  is free to move along an axis X and an axis Y. The X axis is as shown while the Y axis is orthogonal to the X axis and into the page of FIGS. 1 and 2.  
         [0019]    As shown in FIG. 3, the airbag inflator  26  is connected to a steering wheel  14  through a flange  39 , which is mounted to a support  54 , a resilient knob such as a piece of rubber, attached to a leg  56 . The leg  56  attaches to s steering wheel armature  57  of the steering wheel  14  as shown. A support  54 , which may comprise a rubber mount for an airbag inflator  26 , permits an airbag inflator  26  to damp vibration of the steering wheel  14  over a wide range of frequencies. The airbag inflator  26  may have a predetermined mass that is related to the particular range of vibration frequencies to be damped. This mass may be determined by known techniques. To achieve this mass, mass in addition to that needed by the inflator may be added.  
         [0020]    While a gap  30  permits movement of the airbag inflator  26  along axis X to act as a vibration damper at inflation, it also permits the escape of gas from the airbag inflator into a passenger compartment of a vehicle. This gas tends to be extremely hot. Given the proximity of the driver to the steering wheel  14 , it is undesirable to allow this hot gas to escape.  
         [0021]    This problem is solved by the shield  34 , which surrounds the airbag inflator  26  as shown in FIG. 2. The shield  34  may be disposed between the airbag housing  22  and the airbag inflator  26  so as to be in the direct path of the gas escaping from the airbag inflator  26  along arrows A and B through the nozzles  32  of the airbag inflator  26 . The shield  34  may be made of metal, such as steel, having a thickness between 0.5 mm to 1 mm. The metal may be capable of deforming at pressures between 1,500 to 2,000 PSI, the pressure of gas released from nozzles  32 . The pressure increase may be from 0 PSI to  2 , 000  PSI in less than 5 milliseconds upon activation of the airbag. The exact thickness of the shield  34  will vary with the metal selected and the pressure of gas released from the inflator but may be determined using known techniques. Moreover, the metal should be capable of withstanding the high temperature of the escaping gas from a airbag inflator  26 .  
         [0022]    [0022]FIG. 3 illustrates how the shield  34  the bridges gap  30  between the airbag inflator  26  and the airbag housing  22 . During activation of the airbag inflator  26 , hot gas escapes from the nozzles  32  along such directions as indicated by arrow A and arrow B. As shown, the shield  34  is in the path of the gases, and the gases are directed at the shield. Because the shield  34  is thin, hot gas from nozzles  32  will deform the shield  34  to cover the gap  30  providing a seal  33  between the airbag housing  22  and the airbag inflator  26 . Due to the positioning, this deformation occurs almost immediately when gas flow begins. In this way, hot gas is prevented from escaping into a passenger compartment through the gap  30  and instead deploys the airbag  18  along the arrow Y.  
         [0023]    As shown in FIG. 2, the shield  34  may comprise a first portion  37  attached to a flange  39  of the airbag inflator and second portion  35 , which is free to move and orthogonal to first portion  37 . Generally then, the shield  34  comprises an L shaped circular lip extending around the periphery of the airbag inflator  26 .  
         [0024]    As shown in FIG. 3, the airbag housing  22  is provided with stops  29  to provide a flat surface around which the shield  34  may deform. The stops  29  may comprise a soft thin material, such as tape, that reduces the noise between the airbag housing  22  and the metal shield  34  resulting from the inflation of the airbag  18 . In this way, the shield  34  acts like a door having a first position G and a second position H. The shield  34  would leave a gap open at position G and close the gap at position H.  
         [0025]    [0025]FIG. 4 illustrates an alternative mounting of the shield. As shown, the shield  101  may be mounted to the airbag housing  25  rather than to the airbag inflator  26 . Gas from the airbag inflator  26  would still escape along the directions of arrows A and B but would be permitted to also escape along arrows C and D to cause the shield  101  to deform and contact the stop  103 , thereby closing the gap  105 .  
         [0026]    [0026]FIG. 5 illustrates another way to mount an airbag inflator  26  to act as a damper for a steering wheel  14 . As shown, the airbag inflator  26  is mounted to a support  54 , a resilient rubber mount, which itself is mounted to an airbag housing  69  instead of to an independent leg as shown in FIGS.  1 - 3 . A gap  61  exists between the airbag inflator  26  and the airbag housing  69 , requiring a shield  55 , which selectively bridges a gap  61  upon actuation of the airbag inflator  26 . The shield  55  will contact the stop  59 . The airbag inflator  26  is operatively in contact and in vibration communication with a steering wheel  14  through the airbag housing  69  and the steering wheel cover  60 , permitting the damping of the steering wheel by the airbag inflator  26 .  
         [0027]    [0027]FIG. 6 illustrates an inflator  26  resiliently mounted to the airbag housing  27  through support  63 . In addition, the shield  42  is shown as a dual layer shield comprising a first layer  46  and a second layer  50  with the second layer  50  folded over the first layer  46  while still leaving a portion  65  of the first layer  46 , not overlapped. The dual layer protection provides additional sealing protection across the gap  67  following deformation or bending of the shield  46 . Having a portion  65  of the shield  46  not overlapped by the second layer  50  permits the shield  46  to bend and deform more easily. FIG. 6A shows the shield  42  deformed with the second layer  50  sealing against the airbag housing  27 .  
         [0028]    [0028]FIG. 7 illustrates another shield design comprising a ring  38  having four segments  107 , 109 ,  111  and  113 . Each segment overlaps the other at overlap portions  115 ,  117 ,  119  and  121 . The segments  107 , 109 ,  111  and  113  are not adhered to each other but merely overlap at overlap portions  115 , 117 ,  119  and  121 . In this way, the ring  38  may easily deform segment by segment without the rigidity or resistance to deformation encountered by a non-segmented ring.  
         [0029]    The aforementioned description is exemplary rather that limiting. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determine the true scope and content of this invention.