Patent Publication Number: US-2009218797-A1

Title: Airbag With a Closable Venting Device

Description:
FIELD OF THE INVENTION 
     The present invention refers to a venting device for airbags used in automobiles to cushion the blows suffered by drivers and passengers in the event of crashes or collisions. 
     BACKGROUND OF THE INVENTION 
     Airbags basically consist in a folded bag which inflates rapidly by means of a gas produced by a generator when certain sensing devices detect a collision of the vehicle. The bag is thus deployed in front of the driver or passenger, depending on its location, and prevents their bodies from hitting against any part of the vehicle. 
     In normal bag deployment, the inner pressure produced by the generator when filling it with gas can be high enough as to cause the bag to be so hard that the occupant bounces off it. To prevent this drawback they have been provided with a venting opening in order to reduce the inner pressure of the bag and consequently the possibility of causing injuries when activated. 
     The use of several means for closing this venting opening in order to achieve better control of the inner pressure in the bag than that provided by only changing the size thereof is also known. In this sense the use of patches to prevent the gas from immediately exiting through the discharge opening except when the patch is broken when a certain pressure inside the bag is reached can be mentioned. The art has proposed different types of patches with different means for controlling breaking according to, in a greater or lesser degree, a certain resistance to the gas pressure inside the bag. Thus the presence of the necessary pressure for the bag to perform its protective function is made compatible with the assurance that the gas pressure will not reach an excessive value with a risk for the people for whom the bag deploys. 
     On the other hand, the need has also arisen for venting devices allowing to increase the gas outflow according to the specific characteristics of each collision and the type of passenger affected, and in this sense several venting device solutions are known, providing adjustable surface venting openings, facilitating an increase In the venting area as the pressure inside the bag increases. 
     A new need that has arisen also poses the need for airbags that allow reducing the venting area, even completely eliminating it in certain conditions of the impact, which requires closing mechanisms which must operate in a manner opposite that of the art known to date. The aforementioned traditional patches had to completely cover the outlet opening until the inner pressure of the gas in the bag reached a certain level and then broke, not operating anymore. Now the opposite is required: devices allowing closing the venting opening when it is already open when the inner pressure of the bag reaches certain levels. 
     Some proposals are known to this respect such as those disclosed in Spanish patent ES 2182629, in U.S. Pat. No. 6,139,048 and in US patent application 2004/0090054 which use shifting elements to close the venting opening making. use of the stresses produced in the bag due to the pressure difference combined with the occupant load difference. The present invention proposes a solution to the problem based on different principles. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to achieve an airbag with a closable venting device which for very severe collisions allows partial or total closure of the venting opening after a first phase in which it is open discharging gas. 
     This object is achieved by means of a venting device defined at its upper portion by an area of the bag surrounding the venting opening and at its lower portion by a part joined by its contour to the inside of said area, having in its central portion, opposite the venting opening, a closing element and including a plurality of openings, said area and said part being separated by a separating element made from a resilient material and configured such that a chamber is formed between them which receives the gas from the bag through the openings located in said part and discharges it through the opening of the bag, being able the venting device to partially or completely reduce the gas outflow by means of partially or completely closing the gas outlet pathways towards the opening of the bag occurring when the closing element is deformed or broken when pressure inside the bag exceeds predetermined limits. 
     An advantage of the present invention is that the operation of the venting device depends solely on the inner pressure of the bag, which is very interesting due to the possibilities of controlling this variable. The final product is stronger since it does not depend on other characteristics such as stresses/deformations. 
     Another advantage of the present invention is that the inner pressure of the bag is more stable as a venting device operation control parameter than other parameters depending on factors such as the manner in which the bag deploys or the location of the occupant with respect to the bag. 
     Another advantage of the present invention is that it facilitates both total closing of the venting opening of the bag and partial closing for those cases of intermediate severity between the conditions of maximum and minimum collision severity. 
     Other features and advantages of the present invention will be inferred from the following detailed description of an illustrative and by no means limiting embodiment of its object based on the attached drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic elevational view of the venting device according to the present invention. 
         FIG. 2  is a schematic plan view of the lower part of the venting device according to the present invention. 
         FIG. 3  is a schematic elevational view of the venting device according to the present invention in the state corresponding to a low severity collision. 
         FIG. 4  is a schematic elevational view of the venting device according to the present invention in the state corresponding to a medium severity collision. 
         FIG. 5  is a schematic elevational view of the venting device according to the present invention in the state corresponding to a high severity collision, showing a cylindrical deformation of the closing element. 
         FIGS. 6 and 7  are similar views to Figure showing closing elements with tronco-conical and spherical deformations, respectively. 
         FIG. 8  is a schematic elevational view of the venting device according to the present invention in the state corresponding to a high severity collision, using a breakable closing element. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     The venting device of the airbag according to a preferred embodiment of the present invention is formed by an upper area  11  and a lower part  13  separated by a separating element  15  defining a chamber  21 . In a preferred configuration the separating element  15  is a circular annulus. 
     The upper area  11  is formed by a portion of the bag  23  of the airbag inside which the venting opening  25  of area A is located. 
     Area A must be gauged in order to achieve sufficient gas discharge in general airbag operating conditions, since the closing device will only operate in exceptional cases and must therefore be greater than or equal to the area V required for the bag to operate correctly in conditions of less severe collisions. The lower part  13 , preferably made with the same material as the bag, although a material less resilient could also be used, has in its central portion, opposite the venting opening  25 , a closing element  31  made from a resilient material, preferably silicone, and includes a plurality of openings  41 ,  43 ,  45 ,  47  of area B, gauged so as to discharge the amount of gas required in conditions of less severe collisions. 
     Part  13  is joined to the bag  23  along its contour  19  by means of a layer  49  of adhesive material. It may be alternatively joined by sewing, ultrasounds or any other production process. For its part, the closing element  31  is joined by means of an adhesive or any other suitable means to part  13  along the contour of the opening provided for that purpose in its central portion 
     In conditions of less severe collisions there will be a certain inner pressure P 1  inside the bag determining the ventilation area V required for suitably restraining the occupant. Therefore, the sum of the areas B of the openings  41 ,  43 ,  45 ,  47  must be equivalent to area V. In  FIG. 3  it can be observed that, in this case, the gas enters the chamber  21  through the openings  41 ,  43 ,  45  and  47  and exits through the venting opening  25  following the direction indicated by the arrows. The inner pressure P 1  of the bag is not enough to deform the closing element  31  which remains, so to speak, in its rest position. 
     In conditions of intermediate severity there will be greater inner pressure, called P 2 , inside the bag than in the previous cases, and consequently less amount of gas must be discharged, which is achieved by means of the partial closing of the gas outlet pathways occurring with the partial deformation of the closing element  31  due to P 2 , as can be seen in  FIG. 4 . 
     In conditions of more severe collisions a greater inner pressure, called P 3 , occurs inside the bag than in the previous cases, deforming the closing element completely and covering the venting opening  25 , preventing the air from exiting the bag, as can be seen in  FIG. 5 . 
     It must be mentioned that the function of the separating element  15  is that of creating the chamber  21  allowing the closing element  31  to have enough room to be deformed In the mentioned manner, and that it must be made in a resilient material so that it does not make the bag rigid in the area occupied by the venting device, allowing the bag to be folded. On the other hand, said material bust be stable in the operating and temperature conditions required for airbags. They will be preferably made of silicone. 
     The closing element may be constituted by a sheet having different widths in different areas of the sheet. Depending on its size, the shape of the sheet deformation can be different. While the closing element  31  is configured for having a cylindrical deformation, closing elements  33  and  35  are configured for having, respectively, a tronco-conical and a spherical deformation. 
     In accordance with the deformation shape of the closing element under the bag internal pressure, the venting opening  25  and the needed separation in chamber  21  will be sized for obtaining the maximum closure. 
     In an alternative embodiment, it can be used a closing element  37  configured so that, when the internal pressure in the bag reaches a predetermined level (P 3 ), a part of it is broken forming a tab that closes the venting opening  25  as it is shown in  FIG. 8 . 
     Although various embodiments of the invention have been described and represented it is obvious that modifications may be introduced therein that are comprised within the scope of the invention, the latter not being considered limited to said embodiment but rather to the content of the following claims.