Abstract:
An airbag assembly ( 10 ) has an airbag ( 40 ), a tubular inflator ( 20 ) and a rolled heat shield ( 50 ) wrapped about the inflator ( 20 ) and interposed between the inflator ( 20 ) and the airbag ( 40 ). The rolled heat shield ( 50 ) completes at least one full wrap around and encircling a portion of the inflator ( 20 ) wherein the portion of the inflator wrapped by the heat shield ( 50 ) includes one or more gas outlets ( 24 ). The heat shield ( 50 ) preferably is a fabric material.

Description:
FIELD OF THE INVENTION 
     This invention relates to airbag assemblies generally, more particularly to an assembly with a heat shield and diffuser combination affixed to an inflator. 
     BACKGROUND OF THE INVENTION 
     Gas generators are commonly used to provide inflation gas to fill the inflatable cushion or airbag. These inflators come in a variety of shapes and sizes. Some use pressurized fluids contained inside the inflator, some use solid propellants, others use a combination of both of these. 
     When the solid propellant is ignited using an electrical discharge to fire a squib, large amounts of inflation gases are generated very quickly. The inflator rapidly experiences a high pressure and rapid heating. Hot gases are expelled through outlets and fill the airbag rapidly. In addition to the hot gases burning particles and small debris also can be expelled. In some cases internal filters are used to capture the debris. The internal surface of the cushion is often coated with a heat resistant barrier to protect the cushion. In many cases the inflator is placed in a housing structure to secure the inflator and further protect the cushion airbag and the surrounding area. 
     In seat airbag designs, the inflator is tubular in shape. This inflator is held by a steel stamped retainer bracket and clamp ring with clinched studs and locking washers as shown in prior art  FIG. 1 . This assembly requires several components that contribute to cost and assembly complexity. 
     It is an object of the present invention to eliminate components and to provide a superior heat shield protection against hot gases and burning particles. It is a further objective to have this heat shield function as a diffuser that can allow gases to be directed outwardly to fill the cushion. 
     These and other objectives are achieved by the present invention as described and shown. 
     SUMMARY OF THE INVENTION 
     An airbag assembly has an airbag, a tubular inflator and a rolled heat shield wrapped about the inflator and interposed between the inflator and the airbag. The rolled heat shield completes at least one full wrap around and encircling a portion of the inflator wherein the portion of the inflator wrapped by the heat shield includes one or more gas outlets. The heat shield preferably is a fabric material. 
     The fabric material can be made in layers or wrapped about the inflator a plurality of times to form layers. The inner layers are sacrificial layers destroyed as inflation gases are expelled. The fabric material has a 840 denier or greater. 
     The inflator has a housing with two studs for attachment to a vehicle structure. The heat shield is secured to at least one of said studs. The heat shield has two or more openings for positioning over the at least one stud. 
     The heat shield is a fabric material with a length and a width and upon assembly to the inflator the length is wrapped a plurality of times about the inflator to form layers and the width of the fabric is sized to extend covering at least a portion of the inflator having gas outlets. The airbag has a neck portion with an opening to receive the inflator with the wrapped heat shield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by way of example and with reference to the accompanying drawings in which: 
         FIG. 1  is a prior art seat mounted airbag assembly shown in an exploded view. 
         FIG. 2  is a seat mounted airbag assembly of the present invention shown in an exploded view. 
         FIG. 3  is a plan view of a tubular inflator with two mounting studs affixed to an inflator housing. 
         FIG. 4  is a plan view of a tubular inflator with the wrapped heat shield covering the nozzle or gas discharge openings made according to the present invention. 
         FIG. 5  is an end view showing the neck opening of the airbag with the inflator with a wrapped heat shield positioned inside. 
         FIG. 6  is a plan view of the unwrapped heat shield showing the length and width of the material. 
         FIGS. 7A and 7B  are illustrations of a deploying airbag gas flow from the inflator with a wrapped heat shield according to the present invention. 
         FIG. 7A  is an orthogonal view showing the inflating air bag and the up/down direction of the primary gas flow. The horizontal arrow shows the direction of airbag movement into the occupant but one that&#39;s slowed in view of the up/down direction of gas flow. The heat shield is shown and the single oval is the airbag. 
         FIG. 7B  is a side view showing the leaning occupant (this was also the case with the top view). The heat shield is also shown in the lower figure, the dotted oval is the airbag as it is inflating, the solid oval “schematically” shows a more fully inflated air bag. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a seat airbag assembly  100  is shown in an exploded view. The airbag assembly  100  has a wiring harness  30 , a retainer clamp bracket  90 , a ring clamp  92  with projecting stud for passing through the retainer clamp bracket  90 , a lock washer  91  and an inflator  200 . In addition, the airbag cushion  40  is shown in a folded state represented by the rectangular box to the right of the inflator  200 . Upon assembly, the inflator  200  is passed into the clamp ring  92  and the nozzle end is inserted through an end of the bracket  90  in such a way to hold it into position; then the entire assembly is connected and mounted into a structure of a vehicle seat. As can be appreciated, these several components require additional manufacturing costs and time during the assembly process. 
     With reference to  FIG. 2 , a new concept for a seat airbag assembly  10  is shown using the same wiring harness  30 ; however, in this case the inflator  20  has a housing structure  21  with two studs  22  welded to the structure  21  and the airbag cushion  40  is shown again as a rectangular box. This creates an entire assembly  10  for the seat airbag design. 
     In order to use this new design, it is important that the nozzle end  24  of the inflator  20  be covered or protected in such a fashion that particles and burnt debris do not spew outward during emission of the gas generating inflator  20  that would cause the particles to burn through the airbag cushion  40 . 
     As shown in  FIG. 3 , an enlarged view of the inflator  20  is shown wherein the studs  22  are shown welded to the housing  21  and at the one end is the gas discharge nozzle  24 . It is from this discharge nozzle  24  that the inflation gases spew outward to fill the airbag cushion  40 . 
     With reference to  FIG. 4 , a heat shield wrap  50  is shown wrapped about the end of the inflator  20  with the nozzle  24 . As shown in  FIG. 4 , this heat shield wrap  50  encircles the entire nozzle end  24  and is wrapped in several layers; each layer is secured and positioned over a stud  22  on the inflator  20  housing structure  21 . This insertion over the stud  22  through openings  52  in the heat shield wrap  50  allows the wrap  50  to be securely positioned on the inflator  20  such that upon assembly to the seat when the studs  22  are bolted to the seat, the heat shield wrap  50  is simultaneously secured to the structure between the seat and the inflator  20 . 
     With reference to  FIG. 5 , to better appreciate how this works the inflator is shown inside the neck  11  of an airbag cushion  40 . The inflator  20  with the heat shield wrap  50  is positioned inside the airbag  40 , the stud  22  projects through a reinforcement member  14  on the airbag  40  as illustrated to help secure the airbag cushion  40  to the seat assembly. The reinforcement member  14  can use any acceptable method of reinforcement such as an additional layer. In the illustrated embodiment, the reinforcement member  14  is a strap. 
     With reference to  FIG. 6 , the heat shield wrap  50  is shown in a plan view. As illustrated, there is a plurality of holes  52  spaced in such a fashion that as the heat shield  50  is wrapped about the inflator  20  the holes  52  will align with the stud  22  and will be inserted over the stud  22 . This ensures that the entire heat shield wrap  50  can be wound several times about the inflator  20 , thus covering that portion of the inflator  20  with the nozzle or gas discharge opening  24 . 
     Upon initiation of the inflator  20 , a pyrotechnic squib is fired through the wiring harness  30  in such a fashion that the propellant inside the inflator  20  is ignited generating gases. These gases spew out of the nozzle  24  and burnt particles and other debris may also be ejected from the inflator  20 . The heat shield  50 , being formed out of a fabric material wound in layers about the inflator  20 , creates sacrificial layers that may be destroyed adjacent the inflator  20  as the gases are being discharged; however, due to the fact that the heat shield  50  is wrapped, the gases are not prevented from spewing into the airbag as the wrap can be loosely or semi loosely wound about the inflator  20  so that between the adjacent layers on the inflator  20  there are sufficient gaps to allow the inflation gases to be expelled quickly into the airbag  40 , thus not limiting the time to fill the airbag  40 , but rather providing tremendous protection against flying burnt particles which impinge the inner layers of the heat shield  50 . It is important that the wrap  50  provide not only heat shield protection, but act as a diffuser for the gases exiting the nozzle  24 . This diffuser function can greatly be achieved by the tightness of the wrap by having the wrap wound sufficiently tight to keep it secure and yet sufficiently loose so the space between the inflator  20  and the adjacent layers allows the gases to freely permeate out through the ends of the heat shield  50  rapidly when filling the airbag  40 . 
     As can be easily appreciated, the fabric material can be provided as an open woven material that easily lets gas expel or can be provided with some heat shield coating if so desired or believed needed. It is important to understand that the wrap  50  only needs to cover a small portion of the inflator  20 , that portion that allows the escaping gases to exit the device. As a result, it is believed that if the length of the fabric is sufficient to wrap two or more times, preferably three or more times, then a sufficient number of layers will be achieved. The width accordingly only needs to be as wide as needed to cover the escaping gases. As shown in the exemplary of  FIG. 6 , the length is approximately 330 mm and the width is approximately 60 mm. The width and length dimensions are only one example, these dimensions can be any suitable measurement for the particular application being used to provide the necessary heat shielding capability. As shown openings  52  are provided along the length so that the wrap  50  can be secured over the studs  22 . These openings  52  are approximately 6.5 mm in diameter and will fit over the studs  22  very conveniently. These dimensions are exemplary and it is understood can vary based on the shape and size of the inflator  20 . 
     This invention has benefit with an out-of-position occupant  2 , for example one seated on a seat  4  leaning on a window. The looped construction of the heat shield urges inflation gas to flow up and down and avoids accelerating the bag toward the occupant in view of the directions of gas flow. Therefore, this wrapped fabric works as a countermeasure to direct the deploying airbag  40  acceleration up and down as inflation gases flow outward of the inflator  20  and wrapped heat shield  50  as shown in  FIGS. 7A and 7B . 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.