Abstract:
A safety device housed in a motor vehicle and used in the field of automobile safety has an impervious inflatable metal bag fixed to a support, a pyrotechnic charge, and an ignition device intended to be connected to a source of electrical current. The bag includes a first metal sheet which has a central orifice, an intermediate fixing zone attached to the support and a peripheral fixing zone and a solid domed second metal sheet which has a peripheral fixing zone. The two metal sheets are fixed together at their peripheral fixing zones. The pyrotechnic charge is contained in the bag.

Description:
This is a Division of application Ser. No. 09/655,068 filed Sep. 5, 2000, now U.S. Pat. No. 6,460,873. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to the field of automobile safety and relates more particularly to a safety device intended to protect an occupant of a motor vehicle in a collision. 
     2. Description of Related Art 
     For about the last thirty years it has been proposed that the gas-generating systems be incorporated into motor vehicles to inflate conventional textile airbags intended to protect the face and torso of motor vehicle occupants in order to limit as far as possible the risk of bodily injury to which these occupants are exposed in the event of a frontal or side impact. Sometimes, as described for example in German patent application DE 41 16 880, the interior surface of these bags is even coated with a pyrotechnic lacquer. 
     Recently, in addition to these conventional protective devices, car manufacturers have wished to incorporate numerous safety devices aimed, on the one hand, at protecting the lower limbs of the occupants and at reducing the risk of submarining and, on the other hand, at strengthening the actual structure of the vehicle. In this type of application, the safety devices have to operate in extremely short spaces of time and it is therefore necessary to employ highly efficient pyrotechnic charges which, in very short spaces of time, generate the necessary volume of gas. These gases are often toxic and are often at a very high temperature. Conventional textile airbags must therefore not be used because they are liable, on the one hand, to be damaged by the very hot gases and, on the other hand, because of their porosity, to allow the toxic gases to pass into the cabin of the vehicle. 
     To alleviate this problem, safety devices each comprising a conventional gas generator connected to an impervious inflatable metal bag via a gas duct have therefore been proposed, as described in U.S. Pat. No. 5,615,914 and U.S. Pat. No. 5,839,756. However, the use of a gas generator as a separate component makes these safety devices bulky overall and too heavy, making them difficult to incorporate in great number into a vehicle. 
     The person skilled in the art is therefore still in search of a compact and lightweight safety device which will allow the use of highly efficient pyrotechnic charges. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to answer this problem and the invention therefore relates to a safety device housed in a motor vehicle and which comprises: 
     i) an impervious inflatable metal bag fixed to a support, 
     ii) a pyrotechnic charge, 
     iii) an ignition device intended to be connected to a source of electrical current, characterized in that, 
     iv) the impervious inflatable metal bag consists of a first metal sheet which has a central orifice, an intermediate fixing zone attached to the support and a peripheral fixing zone and of a solid domed second metal sheet which has a peripheral fixing zone, the two metal sheets being fixed together at their peripheral fixing zone, 
     v) the pyrotechnic charge is contained in the impervious inflatable metal bag. 
     As a preference, the support consists of a cylindrical body having a flat top surface to which the first metal sheet of the impervious inflatable metal bag is fixed. This body may moreover be made using two distinct elements, the first element corresponding to the bottom part of the said body and the second element consisting of a plate attached to the said first element. 
     Also as a preference, a perforated piece, contained in the impervious inflatable metal bag and fixed into the flat top surface of the cylindrical body, holds the pyrotechnic charge in place. 
     According to a first preferred alternative form of embodiment, the pyrotechnic charge is produced in the form of at least one flat sheet, the said flat sheet being wedged between the perforated piece and a spring, itself bearing against the flat top surface of the body. 
     According to a second preferred alternative form of embodiment, the pyrotechnic charge consists of loose powder. 
     Advantageously, the pyrotechnic charge consists of a composite pyrotechnic composition comprising a silicone binder and an inorganic oxidizing charge, such as a mixture of ammonium perchlorate and sodium nitrate, for example. 
     According to a first preferred embodiment of the invention, the cylindrical body has a radial opening itself extended by a central recess located facing the central orifice borne by the first metal sheet. 
     According to a first alternative form of the first preferred embodiment of the invention, the ignition device, which consists of an electropyrotechnic igniter itself inserted into an electrical connector, is fixed into the radial opening of the cylindrical body. 
     According to a second alternative form of the first preferred embodiment, the ignition device consists of a pyrotechnic transmission cord and of a pyrotechnic relay charge. Advantageously, the pyrotechnic relay charge is housed in the radial opening borne by the cylindrical body, and the pyrotechnic transmission cord has one end inserted in the said radial opening and in contact with the pyrotechnic relay charge. 
     A safety device as described in this first preferred embodiment of the invention is very compact because, at rest, the maximum height of the said safety device corresponds only to the sum of the height of the body and of the maximum distance separating the first metal sheet from the solid domed second metal sheet. 
     According to a second preferred embodiment of the invention, the cylindrical body consists of a discoid plate which has a side wall, there being, passing through the said discoid plate, a radial channel which starts in the said side wall and ends in at least two widened terminations in the flat top surface. It may prove necessary to increase the number of widened terminations depending on the mass of the pyrotechnic charge employed. 
     As a preference, the radial channel contains two electrodes which conduct electrical current and each of the two widened terminations of the radial channel contains an ignition bead electrically connected to the two electrodes. 
     A safety device as described in this second preferred embodiment of the invention is even more compact because the body is in fact reduced to a discoid plate of small thickness. 
     In general, it may be advantageous to place seals between the first metal sheet and the flat top surface of the cylindrical body. 
     The present invention also relates to the use of one or more safety devices as described hereinabove: 
     at the front of the seat part of a passenger seat to raise this passenger in the very first moments following a collision, which makes it possible to greatly reduce the risk of submarining, 
     in the bottom part of the dashboard so as to protect the lower limbs of the front-seat passengers of the vehicle in a collision, 
     to strengthen certain parts of the structure of the vehicle in a collision, for example the bumpers and/or the side doors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Four embodiments of a safety device according to the invention are described hereinafter in FIGS. 1 to  4 . 
     FIG. 1 is a sectioned view of a safety device according to the first alternative form of the first preferred embodiment of the invention. 
     FIG. 1 bis  is an enlarged part view of the safety device depicted in FIG.  1 . 
     FIG. 2 is a sectioned view of a safety device according to the second alternative form of the first preferred embodiment of the invention. 
     FIG. 2 bis  is an enlarged part view of the safety device depicted in FIG.  2 . 
     FIG. 3 is a sectioned view of a safety device according to the second preferred embodiment of the invention. 
     FIG. 3 bis  is an enlarged part view of the safety device depicted in FIG.  3 . 
     FIG. 4 is a sectioned view of a safety device in which the pyrotechnic charge consists of loose powder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1,  1   bis ,  2  and  2   bis , it can be seen that a safety device  1  according to the first alternative form of the first preferred embodiment of the invention or that a safety device  101  according to the second alternative form of the first preferred embodiment of the invention consists of a cylindrical body  2  which, on the one hand, contains an ignition device  3  or  103  which will be described in detail later on and, on the other hand, has a flat top surface  4  to which an impervious inflatable metal bag  5  containing a pyrotechnic charge is attached. 
     More specifically, the cylindrical body  2  consists of a lower first element  7  which has a radial opening  8  extended by a central recess  9  and of an upper second element produced in the form of a circular plate  10  with a central perforation. The lower element  7  and the circular plate  10  are fixed together by welding and in such a way that the central recess  9  lies facing the central perforation of the circular plate  10 . 
     The pyrotechnic charge, which consists of a composite pyrotechnic composition comprising a silicone binder and an oxidizing charge based essentially on ammonium perchlorate and sodium nitrate, is produced in the form of a flat sheet  6  which is wedged between a spring  14  and a perforated piece  15 . The spring  14  is placed so that it bears against the flat top surface  4  at a circular internal indentation surrounding the central perforation borne by the circular plate  10 . The perforated piece  15  has the shape of a cup comprising a peripheral annulus  16  attached by welding to the top surface  4 , a side wall with orifices  17  and a central disc  18  which has bosses  19  in contact with the flat sheet  6 . 
     The impervious inflatable metal bag  5  consists of a first metal sheet  20  and of a solid domed second metal sheet  21 , the two metal sheets  20 ,  21  being made of steel. More specifically, the first metal sheet  20  has a central orifice allowing it to encircle the annulus  16  of the perforated piece  15  and has an intermediate fixing zone  22  which is fixed by threaded fasteners into the circular plate  10  using bolts  23 . The first metal sheet  20  and the second metal sheet  21  each have a peripheral fixing zone  24 ,  25  and are fixed together by welding at their peripheral fixing zone  24 ,  25 . 
     Referring to FIGS. 1 and 1 bis , it can be seen that the ignition device  3  of the safety device  1  is formed using a conventional electropyrotechnic igniter  11  which has an ignition head  12  and which is incorporated into an electrical connector  13 . The ignition device  3  thus formed is inserted in the radial opening  8  in the lower element  7  in such a way that the ignition head  12  is located in the central recess  9 . Electrical power can then be supplied via an electrical circuit which has a first end which plugs into the electrical connector  13  and a second end connected to a central control unit. 
     Referring to FIGS. 2 and 2 bis , it can be seen that the ignition device  103  of the safety device  101  consists of a flexible pyrotechnic transmission cord  130  which is shown not in section in said FIGS. 2 and 2 bis , and of a pyrotechnic relay charge  131 . More specifically, the pyrotechnic relay charge  131  is housed in the radial opening  8  near the central recess  9 . The flexible pyrotechnic transmission cord  130  has, on the one hand, a threaded first end  132  which is introduced into the radial opening and which is in contact with the said pyrotechnic relay charge  131  and, on the other hand, a second end intended to be connected to a central control unit. 
     In operation, the safety devices  1  and  101  act as follows. When the central control unit detects a collision entailing the triggering of the said safety device  1  or  101 , it activates the corresponding ignition device  3  or  103 . The latter generates hot gases in the central recess  9  of the lower element  7  and these gases pass through the central perforation in the circular plate  10  to finally initiate the combustion of the flat sheet  6  constituting the pyrotechnic charge. By combustion, this then, in a very short space of time, produces hot gases which pass through the orifices  17  of the side wall of the perforated piece  15  and allow the impervious inflatable metal bag  5  to be fully inflated, starting from its centre. 
     These safety devices  1 ,  101  are actually very compact because they have a maximum height H of the order of 2 cm. 
     Moreover, depending on the desired location and use of the safety device  1 ,  101 , the first metal sheet  20  and the second metal sheet  21  may have a circular, or rectangular, or even triangular overall shape, for example. 
     Finally, the pyrotechnic charge may also be produced using loose powder contained in a combustible sachet which is itself held in place by the perforated piece  15 . 
     Referring to FIGS. 3 and 3 bis , it can be seen that a safety device  201  according to the second preferred embodiment of the invention consists of a cylindrical body  202  which, on the one hand, contains an ignition device and, on the other hand, has a flat top surface  204  to which an impervious inflatable metal bag  205  containing a pyrotechnic charge is attached. 
     More specifically, the body  202  has the shape of a discoid plate  250 . This discoid plate  250  has a side wall  240  and comprises a radial channel  207  which, on the one hand, begins in the said side wall  240  and, on the other hand, ends in two widened terminations in the flat top surface  204 . The ignition device consists of two electrical wires contained in a sheath  208 , this sheath  208  itself being slipped into the radial channel  207 . A first ignition bead  209  is introduced into one of the two widened terminations of the radial channel  207  and a second ignition bead  210  is introduced into the other widened termination. These two ignition beads  209 ,  210  are connected in parallel to the two electrical wires contained in the sheath  208  and the latter are connected to an electronic central unit. 
     The pyrotechnic charge, which consists of a composite pyrotechnic composition comprising a silicone binder and an oxidizing charge based essentially on ammonium perchlorate and sodium nitrate, is produced in the form of a flat sheet  206  which is wedged between a spring  214  placed bearing against the flat top surface  204  and a perforated piece  215 . The latter has the shape of a cup comprising a peripheral annulus  216  attached by welding to the flat top surface  204 , a side wall with orifices  217 , and a central disc  218  with bosses  219  which are in contact with the flat sheet  206 . 
     The impervious inflatable metal bag  205  consists of a first metal sheet  220  and of a solid domed second metal sheet  221 , the two metal sheets being made of steel. More precisely, the first metal sheet  220  has an orifice allowing it to encircle the annulus  216  of the perforated piece  215  and has an intermediate fixing zone  222  which is fixed by threaded fasteners into the discoid plate  250  using bolts  223 . The first metal sheet  220  and the second metal sheet  221  each have a peripheral fixing zone  224 ,  225  and are fixed together by welding at their peripheral fixing zone  224 ,  225 . 
     In operation, the safety device  201  acts as follows. When the electronic central unit detects a collision entailing the triggering of the said safety device  201 , it delivers electrical current into the two electrical wires and this causes the initiation of the two ignition beads  209 ,  210 . These produce hot gases which come directly into contact with the flat sheet  206  constituting the pyrotechnic charge. This flat sheet  206  then generates hot gases which pass through the orifices  217  of the side wall of the perforated piece  215  and allow the impervious inflatable metal bag  205  to be fully inflated, starting from its centre. 
     This safety device  201  is even more compact than those described previously and has a maximum height h of the order of 1 cm. 
     Furthermore, depending on the desired location and use of the safety device  201 , the first metal sheet  220  and the second metal sheet  221  may have a circular or rectangular or even triangular overall shape, for example. 
     Finally, the pyrotechnic charge may also be produced using loose powder contained in a combustible sachet which is itself held in place by the perforated piece  215 . 
     Referring to FIG. 4, it can be seen that a safety device  301  according to another preferred alternative form of embodiment of the invention consists of a cylindrical body  302  in which an ignition device is fixed, the said body  302  having a flat top surface  304  to which an impervious inflatable metal bag  305  containing a pyrotechnic charge is attached. 
     More precisely, the body  302  has the shape of a plate with a central discontinuity  360 . The latter has a central orifice which is itself extended upwards by a ring. The ignition device, produced using a conventional cylindrical electropyrotechnic igniter  311  fitted with an ignition head  312  and connected to a central control unit, is then inserted into the said central orifice and the ring is then knocked over onto the igniter  311  so that this igniter is held in place by a form of crimping. The cylindrical igniter  311  thus has an axis of revolution which is coincident with that of the safety device  301 . 
     The pyrotechnic charge, which consists of a composite pyrotechnic composition comprising a silicone binder and an oxidizing charge based essentially on ammonium perchlorate and sodium nitrate, is produced in the form of a loose powder  306  which is contained in a combustible sachet (not depicted) wedged between the flat top surface  304  and a perforated piece  315 . The latter is in the shape of a cup comprising a peripheral annulus  316  at ached by welding to the flat top surface  304 , a side wall with orifices  317  and a central disc. 
     The impervious inflatable metal bag  305  consists of a first metal sheet  320  and of a solid domed second metal sheet  321 , the two metal sheets being made of steel. More specifically, the first metal sheet  320  has an orifice allowing it to encircle the annulus  316  of the perforated piece  315  and has an intermediate fixing zone  322  which is fixed by threaded fasteners into the body  302  using bolts  323 . The first metal sheet  320  and the second metal sheet  321  each have a peripheral fixing zone  324 ,  325  and are fixed together by welding at their peripheral fixing zone  324 ,  325 . 
     In operation, the safety device  301  acts as follows. When the central control unit detects a collision entailing the triggering of the said safety device  301 , it activates the igniter  311  which then generates hot gases dispatched directly into contact with the loose powder  306 . By combustion, this powder, in a very short space of time, produces hot gases which pass through the orifices  317  in the perforated piece  315  and which allow the impervious inflatable metal bag  305  to be fully inflated starting from its centre. 
     As described above, the first metal sheet  320  and the second metal sheet  321  may have a circular or rectangular or even triangular overall shape, for example.