Generant preload and tolerance takeup assembly for vehicular airbag installation

Abstract: A metallic preload device for applying a compressive force against an end of gas generant material (38a-c) situated in a cylindrical mesh filter (18) of a gas generator includes a cup-like body (10), a spring (24) which may be a finger spring washer and a gas generant contact member (32) which may be a steel disc washer. Barbs (16) protruding from a cylindrical sidewall (14) of the body (10) engage the filter (18). Components of the device may be held together by a hub (22) or rivet extending from the body (10) through the spring (24) and contact member (32). The contact member may be integral with the spring. In one embodiment all three components are integral and a raised central portion of the body (10) constitutes the contact member and is connected to an outer region of the body by body sections constituting springs.

Description: This invention relates to the field of automotive airbag installations. More specifically, it relates to apparatus for preloading the generant and taking up tolerance differences. The generant which is employed in automotive airbag installations may be any of several types. The charge may be made up of loose pellets, of stacked wafers, or may comprise one or more single extruded grains. In a passenger-side airbag installation, the generant charge is normally installed in a cylindrical ignition can and is surrounded by a cylindrical filter which may be made, for example, from materials such as steel wool to prevent sparks or particles of hot material from entering the airbag. It is necessary to preload the generant charge in order to cushion it from damage due to shock and to prevent looseness that would permit movement under vibration. An additional reason for preloading is the difference in thermal expansion between the aluminum and steel portions of the installation. The ignition chamber is normally aluminum while its internal components are primarily steel. As a result, the aluminum, which has greater heat expansion, is the first to be affected. Although temperature changes during normal operation are usually slow and have little effect on the length differential, the assembly must undergo testing requirements wherein the temperature change conditions are more exaggerated. Most commonly, preload is accomplished by the use of foamed rubberized silicone pads such as disclosed, for example, in U.S. Patent 4,846,368 of Goetz. The problem with using this material is that it is subject to off-gassing and burning. A further gas generant loading arrangement for an airbag inflator (on which the pre-characterising part of claim 1 is based) is described in EP-A-0 324 639. A cup-shaped body is located just inside one end of a cylindrical filter which is housed in a ported cylindrical housing. Mesh cushioning members are interposed between each disc of gas generant material and between the end disc of generant and the cup-shaped body. The cup-shaped body has an outwardly projecting flange which engages one end of the filter and against which part of the housing bears to hold the cup-shaped body in place. Prior to installation in the housing the cup-shaped body will accordingly not be securely retained within the filter. Other arrangements for loading gas generant in a filter positioned in an airbag inflator are described in EP-A-0 589 042. In one embodiment a cup-like leaf spring is held by an initiator against one end of a stack of gas generant wafers and in another embodiment a coil spring is held by a housing end cab against a combustible contact member which in turn bears against the end of the stack of gas generant wafers. In both of these embodiments it is necessary for the filter containing the gas generant wafers to be fitted into the housing before any load on the gas generant can be established. Another problem with prior art preload assemblies is that the preload mechanism is not normally a part of the filter/generant assembly, thereby resulting in a more complex installation than would be desired. Accordingly it is a primary object of the present invention to provide a generant preload which is metallic to preclude off-gassing and burning. Another object is to provide such a preload which is integral with the filter to simplify assembly. Other objects, features and advantages will become apparent from the following description and appended claims. The invention comprises a preload for a vehicular airbag system which includes a hollow cylindrical filter retaining therein a substantially cylindrical gas generant. The preload is seated against one end of the gas generant and includes a metallic cup-shaped body seated securely within one end of the filter. A metallic contact member engages the corresponding end of the gas generant. Metallic spring means are provided between the contact member and the body for maintaining an axial compressive force against the gas generant. The cup-shaped body has a plurality of barbs extending radially from its side wall which are engageable with the filter for securely retaining said cup-shaped body within the first end of the filter upon insertion thereinto. The invention will now be described by way of example only with reference to the accompanying Figures in which: FIG. 1 is an exploded isometric view of a three piece preload in accordance with the present invention; FIG. 2 is an elevational cross-section of the preload of FIG. 1 shown installed at one end of a filter assembly and generant charge; FIG. 3 is a modified version of the preload of FIG. 2 ; FIG. 4 is another version of the preload of FIGS. 2 and 3 ; FIG. 5 is a front view of another modification of the preload of the present invention; FIG. 6 is a cross-section taken substantially along the line 6-6 of FIG. 5 ; FIG. 7 is a front view of the base portion of another modification of the preload of this invention; FIG. 8 is a side view of the base of FIG. 7 ; FIG. 9 is a front view of a spring member usable with the base of FIG. 7 ; FIG. 10 is a cross-section taken substantially along the line 10-10 of FIG. 9 ; FIG. 11 is a cross-section taken substantially along the line 11-11 of FIG. 9 ; and FIG. 12 is a side view of the assembled base portion of FIG. 7 and spring member of FIG. 9 . FIGS. 1 and 2 illustrate a three part preload which might be used, for example, with a gas generant in the form of a plurality of stacked wafers. It comprises a cup-shaped steel body 10 comprising a substantially circular base 12 surrounded by a sidewall 14 . The sidewall 14 is pierced and bent to provide a plurality of radially extending barbs 16 . The barbs 16 are designed to engage the inner surface of a cylindrical filter 18 so that the body 10 is substantially coaxial with the filter 18 along its longitudinal axis 20 . In the illustrated embodiment, the base 12 is not an uninterrupted disc but is formed to provide a central hub 22 . Mounted over the hub 22 and slidable therealong is a steel finger spring washer 24 . A finger spring washer is a commercially available element, comprising an annular disc 26 from which depend spring fingers 28 . An opening 30 in the finger spring washer 24 is sufficiently large to permit movement along the axis of hub 22 . The preload of FIGS. 1 and 2 is completed by an annular steel disc washer 32 which may have a central opening 34 substantially equal to the opening 30 in the finger spring washer. These elements are assembled as illustrated in FIG. 2 , whereupon the end of the hub 22 is expanded to form a cone 36 to retain the elements in a single assembly. One application of the preload of FIGS. 1 and 2 is illustrated in FIG. 2 . As shown therein, the gas generant charge comprises a plurality of stacked wafers 38a-c which are urged compressively against the washer 32 , compressing the spring fingers 28 . Normally the preload of this invention would be installed at only one end of the generant charge. One example of such an installation is described and illustrated in US patent application 08/213,176 of Lauritzen, Green, and Rose which has been assigned to the proprietor of the present application. The disclosure of that application is fully incorporated by reference herein. It will also be apparent, however, that if desired, the preloads could be employed at each end of the generant charge. FIG. 3 illustrates a modified version of the preload of FIGS. 1 and 2 . Its body 40 is essentially similar in many respects including the sidewall 14 and barbs 16 . However, its base 42 is in the form of an annular disc defining a central hole 44 . The finger spring washer 24' and the annular disc washer 32' are basically similar but have smaller central openings. Through these openings passes a rivet-like hub member in the form of a pin 46 having an enlarged head 48 bearing against the washer 32' and an expanded head 50 at its other end serving to retain the preload members together. The FIG. 3 version of the invention is particularly useful when the gas generant comprises a mass of pellets because the end of the preload will close the end of the filter assembly and prevent the escape of any pellets. FIG. 4 illustrates another version of the preload of this assembly. The modified preload illustrated in FIG. 4 is essentially similar to that of FIG. 3 and, accordingly, is given similar reference numerals. However, in this version the central rivet-like member including pin 46 is omitted and the washer 32 is replaced by a disc 52 . In this version the preload may be three separate elements or the elements may be combined by tack welding or other suitable means. A further modification of the invention is illustrated in FIGS. 5 and 6 . This is a one-piece preload which has a body 54 similar to those previously described in that it includes a sidewall 56 with barbs 58 and a circular base 60 . It differs, however, in that the member engaging the generant charge is a raised central portion 62 of the base 60 . The base 60 is drilled to provide a plurality of circumferentially situated circular openings 64 surrounding the raised central portion 62 . This member, similarly to the preloads previously described, is of steel. Accordingly when the raised central portion 62 is depressed by the force of the generant charge, the steel 66 remaining between the openings 64 functions as springs to achieve the objectives of the invention. A still further modification of this invention is illustrated in FIGS. 7-12 . This is a two part assembly. A cup-shaped body 68 is formed from a sheet metal stamping. It includes a planar base 70 having projecting barbs 72 and surrounded by a segmented sidewall 74 . The base 70 defines a central circular opening 76 . The spring member 78 of this modification is illustrated in FIG. 9 . It is formed of a disc 80 of a sheet material such as steel. Four pairs of parallel slots extend to the edge of the disc to form four radial leaf springs 82a-d . These springs are bent downwardly and recurved at their ends into the configuration illustrated in FIG. 10 . A pair of diametrically opposed slots in the disc 80 form a pair of retaining tines 84a,b . Each of the retaining tines is bent downwardly as illustrated in FIG. 11 and then bent again to form a knee 86 . The distance between the two knees is slightly greater than the diameter of the opening 76 in body 68 . The spring member 78 is assembled to the body 68 as illustrated in FIG. 12 . The spring-like retaining tines 84a,b are forced through the opening 76 and snap the spring member into engagement with the body 68 , the leaf springs 82a-d then engaging the base 70 as illustrated. The FIGS. 7-12 version of this invention is illustrated as including four leaf springs and two retaining tines. However, it will be appreciated that this is for illustration only. Any number of either element may be incorporated into the assembly. One important feature of the FIGS. 7-12 modification is that the base 68 may be used without the spring member on one end of the filter assembly if desired.

Claims: A preload device for gas generant (38a...) in an automotive airbag installation of the type wherein the gas generant (38a...) has first and second ends and is housed within a cylindrical filter (18) having first and second ends, which device comprises: a metallic cup-shaped body (10) having a sidewall (14) seatable within the first end of said filter (18) substantially coaxial therewith, and a substantially circular base (12) bounded by said sidewall (14); a metallic contact member (32) engageable with the first end of said gas generant (38a...); and metallic spring means (24) for maintaining an axial compressive force against the first end of said gas generant (38a...), characterised in that: said metallic spring means (24) is intermediate said base (12) and contact member (32); and said cup-shaped body (10) has a plurality of barbs (16) extending radially from its sidewall (14) which are engageable with said filter (18) for securely retaining said cup-shaped body (10) within the first end of said filter (18) upon insertion thereinto. The device of claim 1 wherein said cup-shaped body (10), contact member (32), and spring means (24) are interconnected. The device of claim 1 or 2 wherein said contact member comprises a raised central portion (62) of the base (60) of said cup-shaped body (54) and said spring means comprises portions (66) of said base (60). The device of claim 3 wherein said base (60) defines openings (64) spaced radially thereabout relative to its longitudinal central axis (20) and said spring means comprises the base portions (66) intermediate said radially spaced openings (64). The device of any preceding claim wherein said contact member (62, 80) and said spring means (66, 82a...) are unitary. The device of claim 5 wherein said spring means (82a,...) are leaf springs formed in said contact member (80) and wherein said contact member (80) additionally includes at least one retaining tine (84a, 84b) engageable with said cup-shaped body (68). The device of claim 1 or 2 additionally comprising holding means (22) for maintaining said cup-shaped body (10), contact member (32) and spring means (24) as a unitary assembly. The device of claim 7 wherein said cup-shaped body (10) includes an axial hub (22) constituting said holding means and said contact member (32) and spring means (24) are annular and slidably supported on said hub (22). The device of claim 8 wherein said hub (22) is a substantially cylindrical axial extension of the base (12) of said cup-shaped body (10) and is captured within an axial opening (34) of the contact member (32). The device of claim 7 wherein each of said cup-shaped body (40), contact member (32'), and spring means (24') are annular, have central openings and are interconnected by a rivet-like member (46) constituting said holding means which extends through their central openings. The device of claim 10 wherein said rivet like member comprises: a pin (46) having a first end extending through the central opening (44) in the base (42) of the cup-shaped body (40) and a second end extending through the central opening of the contact member (32'); an enlarged head (50) on the first end of said pin (46) to capture it within said base (42); and an enlarged head (48) on the second end of said pin (46) to capture it within said contact member (32'). The device of claim 1 or 2 wherein said contact member (32) comprises a disc. The device of claim 1 or 2 wherein said spring means (24) comprises a finger spring washer. A gas generating assembly for a vehicular airbag system including a preload device as claimed in any preceding claim, a substantially hollow, cylindrical filter (18) having a longitudinal central axis (20) and first and second ends, a substantially cylindrical gas generant (38) having first and second ends and retained within said filter (18) substantially coaxial therewith, wherein the metallic cup-shaped body (10) is seated securely within the first end of said filter (18) and substantially coaxial therewith with its plurality of barbs engaging said filter (18); the contact member (32) engages the first end of said gas generant (38); and the metallic spring means (24) maintains an axial compressive force against the first end of said gas generant (38).

Inventors: LAURITZEN DONALD R, RALSTON JOSEPH L, LAURITZEN, DONALD R., RALSTON, JOSEPH L.
Applicants: AUTOLIV ASP INC, AUTOLIV ASP, INC. (AN INDIANA CORP.)
Application year: 1995
Main classification: B60R21
IPC codes: B60R21