Extruded generant

Abstract: Vehicle occupant restraint gas generant comprising three cylindrical extruded pieces (28A-C) with longitudinal grooves (32) extending radially inwardly from the surface of the pieces to a depth of at least half of the radius of the pieces and accommodating extruded igniter strips (30) configured so as to conform at least partially to inner surfaces of the grooves (32). The gas generant (28A-C) may be accommodated within a mesh filter cylinder (24) located within a perforated ignition can (20) which is connected by extensions (16, 18) to sidewalls (12, 14) of a reaction canister (10). The ignition can (20) is formed as a one-piece extrusion with the sidewalls (12, 14) and the extensions (16, 18).

Description: This invention relates to motor vehicle airbag restraint systems. A motor vehicle airbag system, and in particular a passenger-side module, customarily includes a trough-shaped reaction canister closed at its ends by endplates. An inflator is mounted within the reaction canister. The inflator normally comprises a cylindrical ignition can having gas ports through its wall. The ignition can encloses a gas generant surrounded by a filtration medium. A folded airbag is enclosed within the reaction canister with its mouth arranged to receive the gases from the generant when activated by a crash sensor. Most prior art inflators include generants that burn from the center outward. They might be, for example, in the form of stacked washer-like wafers having an igniter passing through the central hole. Alternatively, the generant might be in the form of pellets surrounding the igniter. Upon ignition, the gases which are produced exit through gaps between the wafers, through spaces around the pellets, or through gaps between generant sections. These arrangements have worked well in practice. However, the number of individual pieces, both of the generant and the reaction canister, have required expensive fabrication machinery and an undesirable amount of handling and assembly. As a result, the inflator has become the most expensive part of the airbag module. An alternative form of gas generant for an airbag inflator is described in Patent DE-A-3932576. The precharacterising part of claim 1 based on this prior art. The generant is in the form of a tubular or star-shaped extruded grain on a surface of which an explosive coating is provided which acts to transfer ignition along the length of the grain at supersonic speed. The highly sensitive explosive coating is accordingly applied the generant during its production and subsequent tailoring of the gas generant charge is not easily possible. A further example of a prior art arrangement for igniting gas generant material is described in Patent US 3,062,147. The rocket motor described in this patent contains an elongate gas generant body containing a concentric core of an incendiary mixture along the centre of which detonating cord is positioned. The detonating cord comprises an explosive core encased in a metal sheathing which is covered by a strengthening outer layer. The multi-part nature of this ignition system will necessitate a number of fabrication steps. Accordingly it is a primary object of the present invention to provide an airbag module wherein the number of parts is substantially reduced. Another object is to substantially reduce the amount of labor required to assemble such a module. Other objects, features and advantages will become apparent from the following description and appended claims. According to the invention there is provided a vehicle occupant restraint system gas generant comprising an extruded, elongated member having a substantially cylindrical surface and a substantially circular cross section partially subdivided by radial grooves extending along its length, characterised by igniter strips retained within a plurality of said radial grooves. Preferably the igniter strips are also extruded. The main generant charge may extend the full length of the canister or may be assembled with one or more inert sections to control the volume of gas produced. The invention will now be described by way of example only with reference to the accompanying figures in which: FIG. 1 is an exploded perspective view illustrating an airbag module employing gas generant according to the invention; FIGS 2A - 2F illustrate various configurations of the extruded gas generant and igniter strips; and FIG. 3 is a longitudinal cross-section through the airbag module shown exploded in Figure 1. FIG. 1 illustrates in exploded format the various elements which make up a passenger-side airbag module incorporating the present invention. The main body is a reaction canister 10 which includes sidewalls 12 , 14 forming the sides of a trough. The floor of the trough is formed by inwardly extending extensions 16 , 18 of the sidewalls. These sidewall extensions are integral with diametrically opposite sides of a cylindrical ignition can 20 . It is important to note that all of the foregoing elements of the reaction canister 10 are joined in a single member which is preferably extruded and cut to the desired length. The material employed may be, for example, aluminum. The top surface of the ignition can 20 which lies within the trough is drilled or pierced to form a plurality of vent holes 22 . The vent holes 22 permit gas from an activated generant within the ignition can 20 to enter the mouth of an airbag which is contained within the reaction can 10 . As the airbag itself does not form a part of this invention, it is not illustrated. Housed within the ignition can 20 is a hollow cylindrical filter 24 which may be formed, for example, of wire mesh. Enclosed within the cylindrical filter 24 is a gas generant assembly 26 . The gas generant assembly comprises a cylindrical generant charge 28 which may be in one piece or in a plurality of pieces 28a , 28b , 28c as illustrated. Retained in cavities within the generant charge are a plurality of strip igniters 30 . Both the generant charge 28 and the strip igniters 30 may be extruded. The reason for illustrating the generant charge 28 as a plurality of extrusions is to illustrate a "tuned" charge. In such a charge, one section such as central portion 28b may be inert. As a result, the volume of gases produced is reduced without the need for changing the size of the reaction canister. It is desirable for the generant charge to burn for a given period of time and then to burn out with little or no tail off. It is important, however, for the gases to move outwardly normal to the center of the charge, to the ports at the outer periphery of the ignition can 20 . To accomplish these objectives a variety of grain configurations may be employed which permit gases to exit through the outer surfaces of the generant charge. These configurations can also control the production of burned gas, which is desirable during the initial phase of the burn. It is most desirable to obtain low gas production during the first 15 milliseconds of burn followed by maximum gas production to burnout. Various configurations of gas generant cross-sections and strip igniters are illustrated in FIGS. 2A-2F . In each instance, the generally cylindrical generant 28 defines radial openings 32 of various shapes into which are keyed the correspondingly shaped strip igniters 30 . The igniter strips 30 protrude past the generant charge 28 to surround an initiator 41 . The protruding ends may be sensitized to aid ignition. The initiator 41 will ignite the protruding igniter strips which will, in turn, ignite the generant. The generant charge 28 is preloaded to provide cushioning against shock, vibration and thermal expansion. It will also take up any tolerance differences. A preload assembly 34 is provided at one end of the generant charge 28 . It may comprise for example a unitary flat washer 36 and cup 38 with a finger spring washer 40 in between. Such an assembly is described in detail in US Patent Application 08/212258 of D.R. Lauritzen and J.L. Ralston which has been assigned to the proprietor of the present application. The disclosure of that application is incorporated herein by reference. The opposite end of the generant charge 28 abuts a cup member 35 which includes barbs 37 which dig into the filter 24 . The base of the cup member defines a central aperture 39 through which pass the ends of the strip igniters 30 . The reaction canister is completed by endplates 42 , 44 at either end. End bases 46 , 48 of the usual type have flat plates 50 which are screwed to the respective endplates and include cylindrical sockets 52 for receiving the ends of the gas generant assembly 26 and filter 24 .

Claims: Vehicle occupant restraint system gas generant (28) comprising an extruded, elongated member having a substantially cylindrical surface and a substantially circular cross section partially subdivided by radial grooves (32) extending along its length, characterised by igniter strips (30) retained within a plurality of said radial grooves (32). The gas generant of claim 1 wherein the grooves extend to a depth of at least half the radius of said circular cross section. The gas generant (28) of claim 1 or 2 wherein said elongated member is substantially cylindrical and said grooves (32) extend inwardly from said cylindrical surface and terminate at a depth less than the radius of said cylinder. The gas generant of any preceding claim wherein each of said igniter strips (30) has a cross-sectional shape substantially conforming to the shape of its associated groove (32). The gas generant of any preceding claim wherein said igniter strips (30) are extruded. The gas generant of any preceding claim wherein said gas generant comprises a plurality of said extruded elongated members (28a, 28b, 28c) and wherein said members comprise both active and inert members.

Inventors: GREEN DAVID J, LAURITZEN DONALD R, ROSE LARRY D, GREEN, DAVID J., LAURITZEN, DONALD R., ROSE, LARRY D.
Applicants: AUTOLIV ASP INC, AUTOLIV ASP, INC. (AN INDIANA CORP.)
Application year: 1995
Main classification: B60R21
IPC codes: B60R21, C06C9, F42C19