Abstract:
An inflator ( 1 ) is disclosed for use in a safety device within a motor vehicle, for example, for inflating an air-bag. The inflator comprises at least one gas outlet ( 23 ) having an initial predetermined gas flow area. The or each gas outlet incorporates a deformable part ( 41 ) which is configured to deform, in response to a predetermined gas pressure, so as to increase the gas flow area of the gas outlet. The deformable part ( 41 ) may be surrounded by a slot ( 40 ) which initially constitutes the outlet. The deformable part includes a neck ( 42 ) which bends so that the deformable part ( 41 ) opens like a flap. The invention is particularly suited for incorporating in a hybrid multi-stage gas generator comprising two or more pyrotechnic charges that can be actuated in combination or independently. The variable-area gas flow outlet provides an arrangement to vary the cross-section or area of a gas flow passage in response to a high pressure of gas.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     THE PRESENT INVENTION relates to an inflator and more particularly relates to an inflator for use in actuating and deploying a safety device, such as an air-bag, in a motor vehicle in the event that an accident should occur. 
     2. Description of Related Art 
     Many different types of inflator have been proposed previously for use in motor vehicles to actuate or deploy safety devices such as air-bags. In particular, it has been proposed to use gas generators which are termed “adaptive multi-stage inflators” which can be utilised to provide different inflationary effects in response to different types of crash or accident. In such an adaptive multi-stage inflator there may be two or more pyrotechnic charges that can be actuated in combination or independently. One pyrotechnic charge may be actuated before the other pyrotechnic charge, the delay before actuation of the second charge being 5 milliseconds or longer. A short delay may be appropriate for a very “hard” impact and a long delay may be more appropriate for a “light” impact. Many adaptive multi-stage inflators are of the “hybrid” type, meaning that the inflator has not only a pyrotechnic charge, but also a reservoir of compressed gas. 
     There are many important design parameters to take into account when designing an adaptive a multi-stage inflator, including the quantity, composition and configuration of the or each pyrotechnic charge, and the quantity, composition and pressure of the compressed gas if the gas generator is a hybrid gas generator. It is also necessary to provide an appropriate flow regulation for gas emerging from the inflator. Many pyrotechnic materials only provide an optimum “burn” characteristic when subjected to a back pressure and thus, in many cases, the flow of gas must be carefully regulated. 
     Thus, in some adaptive multi-stage inflators, where only a first pyrotechnic charge is to be actuated, the cross-section of the outlet flow path for gas can be relatively small, whereas if two or more pyrotechnic charges are actuated, the cross-section of the outlet flow path must be much greater. If two pyrotechnic charges are actuated within a relatively short period of time, the internal gas pressure may rise to very high levels, and if the cross-section of the outlet flow path is not appropriate, with regard to the quantity of gas being generated, then there is a risk that the parts of the inflator may be damaged. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved gas generator in which the risk of such explosion is minimised or obviated. 
     According to the present invention, there is provided an inflator for use in a safety device within a motor vehicle, the inflator comprising a hybrid multi-stage gas generator; the gas generator including a chamber accommodating compressed gas, a first pyrotechnic unit incorporating a first pyrotechnic charge configured so that, on actuation of the first pyrotechnic charge, hot gas from the pyrotechnic charge is directed into the chamber containing said compressed gas; and a second pyrotechnic unit incorporating a second pyrotechnic charge configured so that on actuation of the second pyrotechnic charge, hot gas from the second pyrotechnic charge is directed into the chamber containing the compressed gas; at least one gas outlet being located in a flow path from the chamber containing compressed gas to the exterior of the inflator, the gas outlet having an initial predetermined gas flow area, the gas outlet incorporating a deformable part configured to deform in response to a predetermined gas pressure, thereby increasing the gas flow area of the gas outlet. 
     Preferably the deformable part comprises a neck joining a tab or flap to a component of the inflator which defines the said gas outlet, the tab or flap being at least partially surrounded by one or more slots which define the initial gas flow area. 
     Advantageously the tab or flap is surrounded by a horseshoe-shaped slot, the neck being defined between the ends of the slot. 
     Conveniently the tab or flap is of substantially square form. 
     Preferably the slot is of substantially “U”-shaped form. 
     Advantageously the slot comprises two parallel slot parts extending from a free end of the said component. 
     Conveniently the tab or flap is substantially triangular. 
     Preferably the deformable part of the or each gas outlet is plastically deformable. 
     Advantageously there are at least three said gas outlets. 
     Preferably the first pyrotechnic unit defines a chamber receiving a pyrotechnic charge, there being a gas flow path leading from that chamber to a plunger such that flow of gas from the chamber will cause the plunger to move, part of the plunger being located adjacent a rupturable foil which initially seals the chamber containing the compressed gas, such that movement of the plunger will rupture the foil, thus permitting compressed gas to flow through the aperture, the or each said gas outlet being provided in a guide tube for the plunger adjacent the said aperture. 
     In order that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic sectional view of a hybrid adaptive multi-stage inflator in accordance with the invention, illustrated in an initial condition, 
         FIG. 2  is a view of the inflator of  FIG. 1  after actuation of one stage thereof, 
         FIG. 3  is an enlarged view of part of the inflator of  FIG. 1  prior to deployment thereof, 
         FIG. 4  is a view corresponding to  FIG. 3  after deployment of the inflator, 
         FIG. 5  is a view illustrating part of a modified inflator in accordance with the invention prior to deployment thereof, 
         FIG. 6  is a view corresponding to  FIG. 5  illustrating the said part of the inflator after deployment thereof, 
         FIG. 7  is an enlarged view of part of another inflator in accordance with the invention, 
         FIG. 8  is an enlarged view of part of yet another inflator in accordance with the invention, and 
         FIG. 9  is an enlarged view of part of yet another inflator in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , a two-stage adaptive hybrid gas generator  1  is illustrated. The gas generator  1  comprises a main cylindrical housing  2 . At one end the cylindrical housing  2  is closed by a first gas generator unit  3 , and at the other end of the cylindrical housing is closed by a second gas generator unit  4 . 
     The first gas generator unit  3  has a cup-shaped housing  5  having a cylindrical side wall  6 , one end of which is closed to form a base  7 , and the other end  8  of which is open. The side wall  6  adjacent the open end  8  is inwardly swaged at a first position  9  around the housing  5 , and is also inwardly swaged at an intermediate position  10  around the housing, between the open end  8  and the base  7  at the closed end  6 . Adjacent the intermediate swaging  10  is provided a plurality of gas outlet apertures  11  through the side wall  6 . Adjacent the gas outlet apertures  11  the housing  5  has a discontinuity  12  where the diameter of the housing is slightly reduced. The base  7  is provided with a central aperture  13  which is initially sealed by means of a rupturable metallic foil  14 . 
     The housing  5  is welded, by means of a weld  15 , to the appropriate open end of the cylindrical housing  2  at a point adjacent the discontinuity  12 . 
     The first swaging  9  adjacent the open end  8  of the cup-shaped housing  5  serves to retain a closure  16  in position. The closure  16  defines a seat which can accommodate a squib which, as will be described hereinafter, will be used to ignite a pyrotechnic charge. An internal chamber  17  is defined between the closure  15  and a locating plate  18  which is held in position by the intermediate swaging  10 . Contained within the chamber  17 , and held in position between the closure  15  and the locating plate  18  is a pyrotechnic charge. 
     The locating plate  18  is a generally planar plate having a protrusion  19  formed on the side thereof directed away from the pyrotechnic charge, the protrusion  19  being centrally located. A gas flow passage  20  extends through the locating plate  18  and the protrusion  19 . 
     A guide tube  21  is provided having one end surrounding and engaging the projection  19  formed on the locating plate  18 . The guide tube  21  extends from the locating plate  18  to the base  7  of the cup-shaped housing  5  and terminates adjacent the central aperture  13  formed therein. A central part of the guide tube  21  is radially inwardly swaged  22 . The end of the guide tube  21  adjacent the central aperture  13  is provided with a plurality of gas outlet apertures  23  which are gas flow ports of adjustable cross-section, as will be described hereinafter in greater detail. 
     Contained within the guide tube  21  is a plunger assembly  24  comprising a piston  25 , the head of which is a sliding and substantially sealing fit within the part of the guide tube  21  extending between the projection  19  formed on the locating plate  18 , and the radially inwardly directed swaging  22 . The piston head is associated with a hollow piston stem  26  which extends through the radially inwardly directed swaging  22 . The hollow piston stem  26  is sealed by means of a plug  27  which is a friction fit within the end of the piston stem  26  remote from the piston head. The plug  27  extends to the central aperture  13  and supports the foil  14  that initially seals the aperture  13 . 
     An annular filter  28  surrounds the guide tube  21 . 
     The second pyrotechnic unit  4  again comprises a cup-shaped housing  30  having a cylindrical side wall  31  which is open at a first end  32 , and which is closed by a base  33  at the other end. The central part of the base  33  is provided with a burst disc  34 , and also with a filling plug  35 . 
     The end of the side walls  31 , adjacent the open end  32  of the housing  30 , are inwardly swaged  36  to retain a closure  37  in position. The closure  37  defines a seat  38  for accommodating a squib. A chamber  39  is defined between the closure  37  and the base  33  of the housing  30  to contain a pyrotechnic charge. 
     A perforated guard  40  is provided which is mounted on the exterior part of the base  33  of the housing  30  to surround the burst disc  34 . 
     The housing  30  is welded to the end of the cylindrical housing  2  opposed to the end on which the first pyrotechnic  3  is mounted. 
     When the various housings described above have been assembled together, initially a mixture of inert gas, such as, for example, 95% argon and 5% helium, is injected into the hollow interior of the cylindrical housing  2  through the filling plug  35  which is then closed. The pyrotechnic charges are located within the chambers  17 ,  39  of the respective pyrotechnic units  3 ,  4 , and the respective closures  16 ,  37  are then located in position together with the appropriate squibs. 
     On actuation of the gas generator  1 , initially the squib mounted in the closure  16  of the first pyrotechnic unit  3  will be actuated to ignite the pyrotechnic charge contained within the chamber  17 . The resultant hot gas will flow through the central gas flow passage  20  provided through the locating plate  18  and the projection  19 , and will act upon the plunger assembly  24 . The gas will force the complete plunger assembly towards the right, as shown in  FIG. 1 . Thus the plug  27  will move to the right causing the foil  14  (initially supported by the plug  27 ) to rupture, thus opening the central aperture  13  formed in the base  7  of the cup-shaped housing  5  of the first pyrotechnic unit  3 . The plunger assembly  24  will move to the right until the piston head engages the inwardly directed swaging  22  formed on the guide tube  21 . The gas pressure within the chamber  17  will then continue to rise to such an extent that the plug  27  will become ejected from the hollow stem  26  of the piston  25  ( FIG. 2 ). Gas is then directed from the chamber  17  through the hollow stem  26  of the piston  25  so that the gas from the chamber  17  is directed well into the chamber defined within the cylindrical housing  2  and becomes admixed with the mixture of inert gas within that chamber. The perforated burst disc guard  40  serves to prevent the burst disc  34  from being physically struck by the plug  27  as it is ejected from the piston stem  26 , into the chamber defined within the cylindrical housing. 
     The mixture of “hot” gas from the chamber  17  and the “cold” gas initially contained within the housing  2 , is allowed to flow towards the left through the central aperture  13  formed in the base  7  of the cup-shaped housing  5 . The gas may flow through the gas outlet apertures  23 , then flowing through the annular filter  28  before emerging through the apertures  11  formed in the side wall  6  of the housing  5 . 
     If the second squib mounted on the closure  37  of the housing  30  of the second pyrotechnic unit  4  is actuated, hot gas will be generated within the chamber  39 . That gas will cause the burst disc  34  to rupture so that the gas from the chamber  39  is also injected into the chamber defined within the cylindrical housing  2 . If the gas pressure within the cylindrical chamber  2  rises to an undesirable extent, the configuration of the gas outlet apertures  23  formed in the end of the guide tube  21  adjacent the aperture  13  formed in the base  7  of the cup-shaped housing  5  will alter so that there is an increase in the available gas flow area, as will be described below in greater detail. Thus the risk of the gas generator or inflator being damaged is obviated or reduced. 
       FIG. 3  illustrates in greater detail the lower end of the guide tube  21  (the annular filter  28  has been removed for the purposes of clarity of illustration). The guide tube  21  extends from the locating plate  18  to the base  7  of the cup-shaped housing  5 . The guide tube  21  is provided, at the end thereof adjacent the base  7  of the cup-shaped housing  5 , with a plurality of radially disposed gas outlet apertures  23 . The outlet apertures  23  are, as will now be described, of variable cross-section. Part of the plug  27  extends beyond the end of the guide tube  21  to support the foil  14  that initially seals the aperture  13 . 
     Each outlet aperture  23  in the embodiment shown in  FIG. 3  is formed by a slit  40  which extends partly along the edge of the free end of the guide tube  21 , and which has two substantially axially extending, but slightly inwardly convergingly directed arms, the slit thus surrounding a generally triangular-shaped tab or flap  41 . The slit  40  has a substantial cross-section so that the slit itself defines an aperture of a predetermined gas flow area, or gas flow cross-section. 
     The tab or flap  41  is formed integrally with the guide tube  21  and is joined to the rest of the guide tube  21  by a relatively narrow neck  42 . 
     Should the pressure within the chamber of the cylindrical housing  2  rise above a predetermined acceptable pressure, the pressure will be such that the tab or flap  41  of each aperture  23  will be driven outwardly with a deformation of the neck  42 . Each tab or flap  41  will then project outwardly, as shown in  FIG. 4 , thus substantially increasing the available gas flow cross-section. Thus, when the pressure rises to an unacceptable level, the apertures  23  automatically adjust so that the apertures are of increased size, helping obviate or minimise the risk of explosion of the inflator. 
     Whilst  FIGS. 3 and 4  illustrate one embodiment of the invention, it is to be appreciated that many alternative designs for the automatically regulating gas flow apertures  23  may be produced. One alternative design is shown in  FIG. 5 , for example. In  FIG. 5 , a guide tube  21  is shown in which the outlet apertures  23  are each constituted by a “horseshoe” or crescent-shaped slot  44  which surrounds a tab or flap  45  having a part circular periphery and which is connected by means of a relatively narrow neck  46  to the rest of the guide tube  21 . It is to be appreciated that for “ordinary” gas pressures within the inflator, gas will flow through the slot  44 . However, if the pressure should rise to an unacceptable level, the tab or flap  45  will be driven outwardly, as shown in  FIG. 6 , so that the aperture  23  then has a much larger gas flow or cross-sectional area. 
     As can be understood from  FIGS. 3 and 4  and from  FIGS. 5 and 6 , in these illustrated embodiments the guide tube is provided with four equi-spaced variable outlet apertures  23 . It is preferred that at least three variable apertures are provided, although five or more may also be found to be suitable. 
       FIG. 7  illustrates a further design for a variable outlet aperture  23 . The aperture, in this embodiment, comprises two totally separate parallel slits  51 ,  52 , which extend axially inwards from the free end of the guide tube  21 . The slits  51 ,  52  define between them a substantially square tab or flap  53  joined to the rest of the tube  21  by means of a “neck”  54  which extends between the ends of the slits  51 ,  52 . Again, under ordinary circumstances, gas will flow through the slits  51 ,  52 , but if a very high pressure is experienced, the tab or flap  53  will be driven outwardly, with a deformation of the neck  54 , to increase the available flow area for gas. 
       FIG. 8  illustrates yet another embodiment in which a substantially “L”-shaped slot  61  is formed at the end of the guide tube  21  to form the variable gas outlet aperture  23 . The slot  61  partially surrounds a tab or flap  62  which is connected to the rest of the tube  21  by means of a relatively narrow neck  63  extending from the end of the slot  61  to the adjacent end of the tube  21 . Again, in this embodiment, under ordinary conditions gas will flow through the slot  61 , whereas if a very high gas pressure is experienced, the tab or flap  62  will be deformed to extend outwardly, thus increasing the available flow area for the aperture  23 . 
     Finally  FIG. 9  illustrates yet another embodiment of the invention in which the variable aperture  23  is defined by a “U”-shaped slot  71  formed adjacent the end of the guide tube  21 . The “U”-shaped slot  71  surrounds a substantially square tab or flap  72  which is joined to the rest of the tube by means of a relatively narrow neck  73 , the neck being parallel to and spaced slightly from the very end of the guide tube  21 . Again, in this embodiment, under ordinary conditions gas will flow through the slot  71  whereas, should a very high gas pressure exist, the tab or flap  72  would be bent outwardly with a consequent deformation of the neck  73  thus increasing the available gas flow area. 
     It is to be appreciated that the variable outlet apertures described above are all formed integrally with the guide tube, without the requirement for any additional components. The variable apertures can thus be provided easily or cheaply. Each gas outlet aperture has an initial predetermined gas flow area, and incorporates a deformable part configured to deform in response to a predetermined high gas pressure, so as to increase the gas flow area of the gas outlet. 
     It is to be understood that the different shapes of aperture may vary the bending effect achieved. A horseshoe-shaped slot will provide a relatively narrow neck, meaning that the tab or flap defined by a horseshoe slot may bend much more easily than a tab or flap defined by two parallel slots. It is possible to treat the area defining the neck to facilitate bending, such as by reducing the thickness of the neck as compared with the thickness of the rest of the guide tube. If the guide tube is formed of metal, the necks may be plastically deformable or resiliently deformable. 
     In the present Specification “comprises” means “includes or consists of” and “comprising” means “including or consisting of”.