Abstract:
In an air-bag arrangement in a motor vehicle a gas generator ( 5 ) has a flange ( 8 ) which is spaced from a flange member ( 3 ) by elongate spacer elements ( 9 ). The spacer elements pass through apertures ( 20, 21 ) formed in an air-bag adjacent a central aperture ( 19 ). On inflation of the air-bag, the part of the air-bag surrounding the aperture will be drawn into an engagement with the flange ( 8 ). Should a very high pressure exist within the air-bag, the part of the air-bag surrounding the aperture will be driven away from the flange ( 8 ), with part of the aperture sliding along the elongate elements ( 9 ), thus permitting excess pressure to be relieved.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   THE PRESENT INVENTION relates to an air-bag arrangement for a motor vehicle and more particularly relates to an air-bag arrangement suitable for mounting in front of an occupant of the motor vehicle in the steering column or the dashboard of the vehicle. 
   2. Description of Related Art 
   It is known to mount an air-bag and a gas generator arrangement in front of an occupant of the motor vehicle such that in an accident situation, the gas generator will inject gas into the air-bag to inflate the air-bag. Thus, as the torso and head of the occupant move forward rapidly, the inflated air-bag provides a cushioning effect to reduce or minimise injury to the occupant of the vehicle. 
   However, a problem arises with such prior air-bag arrangements when the occupant of the vehicle is not fully sitting back in the vehicle seat. For example the occupant of the vehicle may be leaning forward to obtain an item from the glove compartment or may, for any other reason, be sitting forwardly of the seat such that his head and upper torso is relatively close to the air-bag arrangement. 
   If an occupant of the vehicle is leaning forwardly relative to the normal position of an occupant of the seat, the rapidly inflating air-bag will impact with the occupant and further inflation of the air-bag will be resisted or prevented. Consequently the gas pressure within the air-bag will increase to a level much greater than that experienced during unimpeded inflation of the air-bag. Consequently high forces will be exerted on the part of the occupant adjacent the air-bag, which may lead to serious injuries. It is therefore desirable, after part of the occupant has impacted with the air-bag, to reduce gas pressure within the air-bag and consequently to reduce the force exerted by the inflating air-bag on the part of the occupant of the vehicle. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to provide an improved air-bag arrangement. 
   According to the present invention there is provided an air-bag arrangement for a motor vehicle comprising an air-bag, a gas generator having a flange member and an apertured base plate member spaced a predetermined distance away from the flange member, elongate elements being provided extending between the flange member and the base plate member, the air-bag having an opening forming a throat, the air-bag also having a plurality of apertures surrounding said opening, each aperture receiving a respective said elongate element the arrangement being such that, in an accident situation, as gas from the gas generator is introduced to the air-bag, a part of the air-bag adjacent the opening moves into substantially sealing engagement with the flange member of the gas generator and such that, if the inflating air-bag impacts with an occupant of the vehicle, increasing gas pressure within the air-bag moves the part of the air-bag surrounding the opening towards the base plate member so that gas flows from the air-bag through a gas flow path defined at least partly by the space between the flange member and the base plate member. 
   Preferably the elongate elements comprise elongate studs each having a large diameter region inserted through a respective aperture in the air-bag, and a smaller diameter terminal region inserted in an aperture formed in the base plate member. Each stud serves as a spacer between the flange member and the base plate member. 
   Conveniently each stud is provided with a screw thread on which a nut is secured. 
   In one embodiment the elongate elements comprise studs and each stud passes through a bush which serves as a spacer between the flange member and the base plate member. 
   Alternatively the elongate elements comprise tabs which extend from one member to the other member. 
   Alternatively the elongate elements comprise protrusions extending from one member to the other, the protrusions serving as spacers between the flange member and the base plate member. 
   Preferably each protrusion defines an aperture through which a respective stud is inserted. 
   Preferably the throat is dimensioned to receive part of the gas generator. 
   Conveniently the throat is reinforced with an additional layer of material. 
   Advantageously the additional layer of material is formed of a fabric. 
   Alternatively the additional layer of material is formed of metal. 
   Alternatively the additional layer of material is formed of a plastics material. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  is an exploded perspective view of the air-bag arrangement of the current invention; 
       FIG. 2  is a sectional view of the air-bag arrangement taken on line A—A of  FIG. 1  showing the air-bag arrangement in a first condition; and 
       FIG. 3  is a sectional view corresponding to  FIG. 2  but showing the air-bag arrangement in a second condition. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An air-bag arrangement  1  comprises a gas generator  2 , a base plate member  3  and an air-bag  4 . 
   The gas generator  2  comprises a cylindrical housing comprising an upper circular end  5  and a lower circular end  6  interconnected by a tubular side wall  7 . A substantially square flange member  8  extends radially from and surrounds the tubular side wall  7  and separates the first circular end  5  from the second circular end  6 . The flange member  8  is provided with four elongate elements in the form of studs  9  which are substantially equispaced about the flange member  8 . The studs  9  extend from the side of the flange member  8  closest to the second circular end  6  in a direction parallel to the tubular side wall  7  of the gas generator  2 . 
   Each stud  9  has two regions of different diameter. The region  10  of each stud  9  closest to the flange member  8  has a relatively large diameter and the region  11  of each stud  9  remote from the flange member  8  has a relatively small diameter. The small diameter region  11  is provided with a screw thread. 
   Four tabs  12  also extend from the side of the flange member  8  closest to the second circular end  6  in a direction parallel to the tubular side wall  7 . Two tabs  12  are located on one part of the flange member  8  between two of the studs  9  and the other two tabs  12  are located on an opposing part of the flange member between the other two studs  9 . 
   The base plate member  3  comprises a substantially square plate of uniform thickness. The base plate member  3  has a centrally located circular aperture  13  dimensioned to receive the second circular end  6  of the gas generator  2 . The upper surface of the base plate member  3  extends around the circular aperture  13  and is provided with four protrusions  14  which extend upwardly and substantially perpendicularly from the upper surface of the base plate member  3 . Each protrusion  14  is provided with an axial bore  15  which extends through the protrusion  14  and through the base plate member  3 . Each bore  15  is dimensioned and located to receive the smaller diameter region  11  of a respective stud  9 . The upper surface of the base plate member  3  is also provided with four recesses  16  each dimensioned and located to receive a lower portion of a respective tab  12 . 
   The air-bag  4  comprises two fabric layers  17  and  18 , each fabric layer  17  and  18  comprising a circular disc of fabric. The layers of fabric  17  and  18  are superimposed and are connected at their peripheries, for example by a seam. The lower fabric layer  17  is provided with a centrally located circular opening  19  forming a throat. The circular opening  19  is dimensioned and located to receive the lower circular end  6  of the gas generator  2 . Four apertures  20  are formed in the first fabric layer  17  and are equispaced about the periphery of the opening  19 . The four apertures  20  are dimensioned and located such that both regions  10  and  11  of each stud  9  may be inserted through a respective aperture  20 . Four further apertures  21  are also provided about the periphery of the opening  19  and are dimensioned and located such that part of each tab  12  may be inserted through a respective further aperture  21 . 
   In assembling the air-bag arrangement, the gas generator  2  will be inserted through the opening  19  of the first fabric layer  17  so that the gas generator  2  is located within the interior of the air-bag  4 . The gas generator  2  will be aligned with the first fabric layer  17  such that each stud  9  will be inserted through a respective aperture  20  of the first fabric layer  17  and such that each tab  12  will be inserted through a respective further aperture  21  of the first fabric layer  17 . The second circular end  6  of the gas generator  2  may protrude through the opening  19  in the air-bag  4 . 
   The gas generator  2  and the air-bag  4  will then be offered to the base plate member  3 , the base plate member  3  being orientated such that the smaller diameter region  11  of each stud  9  may be inserted through a respective bore  15  on the base plate member  3 . It is to be appreciated that, when so inserted, part of the smaller diameter region  11  of each stud  9  will extend beneath the lower surface of the base plate member  3  and a nut  22  will be screwed onto the screw thread provided on the respective lower region  11  of the respective stud  9 . Each tab  12  will be received within a respective recess  16  on the base plate member  3 . Thus the first fabric layer  17  of the air-bag  4  will be sandwiched between the flange member  8  of the gas generator  2  and the base plate member  3 . It is to be appreciated that the larger diameter region  10  of each stud  9  will space the flange member  8  of the gas generator  2  a predetermined distance from the base plate member  3 . It is also be appreciated that the tabs  12  will also assist in spacing the flange member  8  of the gas generator  2  and the base plate member  3  the same predetermined distance apart. It is envisaged that the predetermined distance apart will be between 2 millimetres and 10 millimetres. 
   It is to be further appreciated that, when the above arrangement is assembled as has been described, the apertures  20  and further apertures  21  provided around the periphery of the opening  19  of the fabric layer  17  of the air-bag  4  are permitted to slide along the studs  9  and the tabs  12  respectively. Thus the part of the first fabric layer  17  of the air-bag  4  adjacent to the opening  19  may move from a position adjacent the flange member  8  of the gas generator  2  to a position adjacent the base plate member  3 . 
   Referring now to  FIG. 2 , in an accident situation, gas will be injected from the gas generator  2  into the air-bag  4  in a direction substantially as shown by arrow  23 . This direction of flow of gas from the gas generator  2  will give the entire air-bag momentum in the direction shown by the arrow  23  and the first fabric layer  17  will be moved along the studs  9  and tabs  12  to a position adjacent and firmly in contact with the flange member  8  of the gas generator  2 . It is to be appreciated that when the fabric layer  17  of the air-bag  4  is in this position, the air-bag  4  is substantially sealed and gas from the gas generator  2  will remain substantially in the air-bag  4 . Thus the air-bag will inflate in a conventional manner. 
   If an occupant of the vehicle is leaning forwardly of the vehicle seat and is thus relatively close to the inflating air-bag  4 , the inflating air-bag  4  will impact with part of the occupant of the vehicle prior to the air-bag  4  being fully inflated. Further inflation of the air-bag  4  in the direction of the arrow  23  in  FIG. 2  will be prevented or restricted and thus gas pressure within the air-bag  4  will increase. The increasing gas pressure within the air-bag  4  will move the part of the air-bag  4  adjacent the opening  19  away from sealing engagement with the flange member  8  of the gas generator  2  to a position adjacent base plate member  3 . This movement will be enabled by the apertures  20  and further apertures  21  sliding along the larger diameter region  10  of the studs  9  and along the tabs  12  receptively. This is the position shown in  FIG. 3 . 
   When the part of the fabric layer  17  adjacent the opening  19  is in the position shown in  FIG. 3 , it is to be appreciated that gas may flow from the air-bag through a gas flow path defined by the space between the flange member  8  of the gas generator  2  and the base plate member  3 , the opening  19  in the air-bag  4  and the aperture  13  in the base plate member  3 . This gas flow path is shown by arrows  24 . This flow of gas from the air-bag will reduce the gas pressure within the air-bag  4  and thus the force exerted by the inflating air-bag  4  on the part of the occupant of the vehicle in contact with the air-bag  4  will be regulated. It is envisaged that this regulation of force will greatly reduce the risk of injuries being imparted to the occupant by the inflating air-bag  4 . 
   It is to be appreciated that, in an alternative embodiment, the spacing between the flange member  8  of the gas generator  2  and the base plate member  3  may be effected solely by the studs  9 , with the tabs  12  being omitted, or solely by the tabs  12 , with the studs being of uniform section along their length. The tabs may be on the base plate member  3  instead of being on the flange member  8 . 
   In a further alternative embodiment each stud  9  comprises a standard bolt of constant diameter which is inserted in a bush prior to being secured to the base plate member  3 . The bushes serve to space the gas generator  2  and the base plate member  3  the predetermined distance apart. 
   In a further alternative embodiment, each protrusion  14  serves as a spacer between the flange member  8  and the base plate member  3 . Each stud  9  comprises a standard bolt of constant diameter which is inserted in a respective aperture  15  formed in each protrusion  14 . When assembled as has been described above, the part of the fabric layer  17  which forms the periphery of each aperture  20  is clamped between the flange member  8  and a respective protrusion  14 . Thus, in an accident situation, the part of the air-bag between each protrusion  14  in an accident situation will move from a position adjacent the flange member  8  to a position adjacent the base plate member  3  to allow gas to flow out of the air-bag. 
   Further, it is envisaged that the periphery of the opening  19  forming the throat of the first fabric layer  17  could be reinforced with an additional layer of material. Such a material could be formed from a fabric, a plastic or a metal material. 
   In the present Specification “comprises” means “includes or consists of” and “comprising” means “including or consisting of”.