Airbag diffuser

Abstract: A diffuser (12) for a supplemental restraint system includes a top wall (24), a cylindrical side wall (22) and a bottom wall (26) defining a substantially cylindrical diffuser chamber having a longitudinal axis. The diffuser (12) is used in a supplemental restraint system having an airbag and a combustion chamber (16) for providing a pressurized gas to inflate the airbag. The bottom wall (26) has an opening (28) having a predetermined flow area, arranged to communicate with the combustion chamber (16) via a burnt disk (34). The diffuser (12) includes a plurality of elongated slots (40) formed therein by lancing, that are generally parallel to the diffuser axis. The slots (40) are configured, and have a flow area, to rapidly inflate the airbag. The slots are further configured to retain debris generated from the combustion chamber (16) and burnt disk (34) within the diffuser (12) and to prevent the debris from entering the airbag upon inflation. The slots (40) are preferably formed by lancing that forms first and second flash portions (54,56) on an interior of the cylindrical side wall (22) that remain connected to and intact with the side wall (22) upon formation.

Description: This invention pertains to diffusers for supplemental restraint systems or airbags. More particularly, this invention pertains to a one-piece airbag diffuser having a plurality of slotted openings for distributing or diffusing the airbag combustion gas products. Supplemental restraint systems or airbags have become an important safety feature in today's automobiles. Airbag deployment technology currently uses a controlled combustion or an explosion to rapidly deploy the airbag. The chemicals that create this controlled explosion are housed in a combustion chamber or housing. The combustion gas products are expelled from the chamber through a diffuser into the airbag to deploy or inflate the airbag. A number of techniques are known to inflate the airbag, such as the use, through combustion, of powdered sodium azide. The combustion reaction creates an instantaneous increase in pressure of between about 800 bar (12,000 pounds per square inch (psi)) and about 1066 bar (16,000 psi). This instantaneous pressure increase inflates the airbag. Airbag deployment requires proper diffusion of the combustion gases to inflate the airbag. One known deployment system includes a combustion chamber, for carrying out and containing the combustion process. The chamber includes an opening in an end thereof for directing the combustion gases. The combustion chamber is mounted or connected to a diffuser, at the opening in the chamber, that is in flow communication with the interior region of the airbag. The diffuser extends into the airbag and diffuses or distributes the gases generated from the combustion process within the airbag to properly deploy the bag. The diffuser must have sufficient open or flow area to permit the gases to flow from the combustion chamber into the airbag to rapidly and properly deploy the bag. A pyrotechnic device for inflating an airbag is disclosed in GB-A-2312274 which shows the features of the peamble of claim 1. This device includes a substantially cylindrical member having a top wall, a cylindrical side wall and a bottom wall defining a diffuser chamber and defining a longitudinal axis, the bottom wall having an opening therein of predetermined flow area for communicating with the combustion chamber; and a plurality of elongated, through-wall slots formed in the cylindrical side wall, generally parallel to the diffuser axis. A burst disk is positioned at about the combustion chamber opening. The burst disk isolates the diffuser from the combustion chamber prior to combustion, and prevents the combustion products from rupturing the wall of the combustion chamber or flowing backward out through the chamber upon deployment. Because of the explosive nature of the combustion process, it has been observed that debris, such as burst disk portions or fragments and combustion product powder particles can be generated. This debris is not intended to enter the airbag upon deployment. Rather, the debris is isolated and remains within the combustion chamber and diffuser subsequent to combustion. One arrangement that is used to retain this debris within the combustion chamber and diffuser includes a generally cylindrical diffuser having a plurality, e.g., eight, large apertures therein and a steel screen positioned within the diffuser. The screen includes a large number of relatively small openings to prevent egress of the debris subsequent to combustion. The diffuser includes a separate end wall that is secured, such as by welding, to the diffuser at the connection to the combustion chamber after the screen is mounted in the diffuser. Although this arrangement works well for its intended function, there are multiple parts and manufacturing process steps required to fabricate the diffuser and to fixedly position the screen within the diffuser. As such, this part can be relatively costly to manufacture. Attempts have been made to utilize other configurations that provide sufficient flow area to assure rapid deployment of the airbag while at the same time maintaining debris within the combustion chamber and diffuser. Such configurations include the drilling or punching a plurality of small openings within the diffusion chamber wall. Such manufacturing processes are, however, costly and can require frequent maintenance of the machining or manufacturing parts. In addition, it has been found that drilling or punching the openings in the diffuser cannot be performed with reliability after the diffuser is fully formed. That is, when the bottom end wall of the diffuser is formed after the openings are drilled or punched, the openings tend to become deformed as a result of the wall formation. Deformation of the openings can result in less than optimal diffusion characteristics for the diffuser. On the other hand, when attempting to punch or drill the openings after the bottom wall is formed, the machining operation can become maintenance intensive. As a result, known diffusers utilize a multiple-piece construction. Accordingly, there continues to be a need for a diffuser that is readily manufactured, and that incorporates debris retaining characteristics while at the same time providing sufficient flow area for rapid deployment of the airbag. Such a diffuser is a one-piece member that is cost-effective to manufacture and it does not adversely effect or increase machine-tool maintenance. According to the present invention a diffuser in accordance with claim 1 for use in a supplemental restraint system includes a top wall, a cylindrical side wall and a bottom wall defining a diffuse chamber. The diffuser defines a longitudinal axis, and is used in a supplemental restraint system having an airbag and a combustion chamber for providing a pressurized gas to inflate the airbag. The combustion chamber has an opening therein for exhausting the pressurized gas. The diffuser is a substantially cylindrical member and includes an opening therein having a predetermined flow area. The opening is adjacent to and separated from the combustion chamber opening. The diffuser has a plurality of elongated, through-wall slots formed therein extending generally parallel to the diffuser axis, the slots being formed by lancing. Preferably, the slots define a total flow area that is greater than or equal to the flow area of the opening in the diffuser bottom wall to rapidly inflate the airbag. In a current embodiment, the diffuser includes sixteen slots. The slots have a generally rectangular shape, and each slot has a height extending parallel to the axis of about 5mm (0.20in) and a width of between about 0.75mm and 1.0mm (0.03 and 0.04 in), for a total flow area of between about 60mm 2 and about 80mm 2 (0.096 and 0.128in 2 ). Preferably, the slots define first and second flash portions from the lancing formation. In a most preferred arrangement, each of the first and second flash portions remains intact with the diffuser, so as to not create cutting debris. Particular embodiments in accordance with the present invention will now be described with reference to the accompanying drawings; in which:- FIG. 1 is a partial cross-sectional view of a diffuser, the diffuser being illustrated mounted to a combustion chamber, with a burst disk positioned at the diffuser opening to the combustion chamber; FIG. 2 is a cross-sectional view of the diffuser of FIG. 1; FIG. 3 is a cross-sectional view of the diffuser of FIG. 2, taken along line 3--3 of FIG. 2; FIG. 4 is a partial view of the diffuser as indicated in FIG. 2; FIGS. 5a-c illustrate various alternate configurations of the diffuser; FIG. 6 illustrates a lancing or piercing tool that is used to form the openings or slots through the diffuser wall; and, FIG. 7 illustrates an exemplary lancing apparatus for forming the slots in the diffuser. Referring now ta the figures, and in particular to FIG. 1, there is shown an exemplary combustion chamber 10 having a diffuser 12 in accordance with the principles of the present invention mounted to an end of the chamber 10. The illustrated combustion chamber 10 is one of a type that is used in the automotive industry for rapid deployment of the supplemental restraint system or airbag. The combustion chamber 10 includes a housing 14 and an internal combustion region 16, and has an opening 18 in an end of the housing 14 for discharging combustion gases. The diffuser 12 is mounted to an end of the combustion chamber 10 over the opening 18. The diffuser 12 is essentially a short, cylindrical element having a cylindrical side wall 22, a top wall portion 24 that may be flat or dished, and a bottom wall portion 26 having an opening 28 therein. The diffuser top wall 24, side wall 22 and bottom wall 26 define a diffuser chamber 30. The diffuser 12 can be mounted to the combustion chamber 10 (as illustrated in FIGS I and 2) at the bottom wall 26 with the opening 28 of the diffuser 12 adjacent to the opening 18 in the chamber 10. In a typical arrangement, a burst disk 34 is positioned over the bottom wall opening 28 at an outer surface 36 of the bottom wall 26. The burst disk 34 isolates the diffuser chamber 30 from the combustion region 16 of the combustion chamber 10. As shown in FIG. 4, in one configuration, the diffuser 10 includes a circumferential lip 38 to which the burst disk 34 is mounted. As is apparent from the drawings, with the burst disk 34 in place between the diffuser 12 and the combustion chamber 10, the diffuser chamber 30 and combustion region 16 of the combustion chamber 10 are isolated from one another. Conversely, when the burst disk 34 is removed or broken, flow communication is established between the combustion region 16 and the diffuser chamber 30. The cylindrical wall 22 includes a plurality of relatively narrow, elongated, through-wall slots or openings 40 formed therein. Preferably, the openings 40 are rectangular in shape, and are formed parallel to a longitudinal axis A of the diffuser 10. The slots 40 are configured to provide sufficient flow area or open area for exhausting the combustion gases from the combustion chamber 10 through the diffuser 12 and into the airbag, to rapidly deploy the airbag. At the same time, the slots 40 are sufficiently small to retain debris that may be generated as a result of the combustion process or reaction within the diffuser 12 and combustion chamber 10 and to prevent debris from entering the airbag. In one embodiment of the diffuser 12 that has an outside diameter of about 25.0 millimeters (mm) (0.986 inches (in)), sixteen slots 40 are formed in the diffuser 12, each slot 40 having a height h of about 5.1mm (0.2in) and a width w of between about 0.762mm (0.03in) and 1.016 mm (0.04in), for a total flow area of between about 62mm 2 (0.096in 2 ) and 83mm 2 (0.128in 2 ). In this embodiment, the slots 40 are equally circumferentially spaced from adjacent slots 40 by an angle ∝, and are thus about 22.5° from respective adjacent slots 40. Those skilled in the art will recognize that other configurations, patterns and quantities of slots 40 can be used to assure proper flow area while maintaining the slot 40 sufficiently small to retain debris in the combustion chamber 10 and diffuser 12 and to prevent debris from entering the airbag. In this embodiment, the opening 28 in the diffuser bottom wall 26 that provides flow communication between the diffuser chamber 30 and the combustion region 16 is circular and has a diameter d of about 7.3mm (0.287in), which results in a flow area of about 51.85mm 2 (0.065in 2 ) when the burst disk 34 is fully removed from the opening 28. Other overall configurations of the diffuser are illustrated in FIGS. 5a-c, in which the diffuser 110 has a flat top wall 112 and a funnel or coneshaped bottom end wall 114 (FIG. 5a), in which the diffuser 210 has a flat top wall 212 and a flat bottom wall 214 (FIG. 5b), and in which the diffuser 310 has a depending insert-type bottom wall 312 (FIG. 5c) that inserts into the neck or top of the combustion chamber 10. It has been observed that although the slots 40 can be formed by various machining techniques such as drilling, punching or the like, it is most desirable to form the slots 40 by lancing, using a lance element or blade 410 such as that illustrated in FIG. 6. Those skilled in the art will recognize that although drilling is a known and accepted method for forming openings in the wall of structural elements such as the diffuser, there are drawbacks to drilling. For example, the machining parts, e.g., the drill bit, can require frequent maintenance to maintain the drill in working order. This is particularly true if the openings are formed after the diffuser is formed, i.e., after the bottom wall is formed. Moreover, if the end walls of the diffuser, and particularly the bottom end wall, is formed after the drilling operation, the openings can become deformed which can adversely effect the flow area across the openings and thus deployment of the airbag. In addition, drilling a series of small holes can be time consuming and can add significantly to the overall cost of fabricating the diffuser. Those skilled in the art will also recognize that although punching the openings can be an effective method for forming the diffuser, punching suffers from some of the same drawbacks as drilling. That is, if the bottom wall is formed after punching the openings, the openings may become deformed and may not hold their dimensions. Again, as with drilling, punches can also require frequent maintenance to assure that they are properly operating. The present lancing process overcomes these drawbacks, and provides additional advantages over drilling and punching methods. As shown in FIG. 6, the lance 410 has first and second essentially mirror image edge portions 412, 414 extending from a central apex 416. As the lance 410 contacts and penetrates the diffuser side wall 22, because the lance 410 is narrow, the material (as illustrated at 50 and 52) that is removed from the wall 22 is separated at the slot 40, in the elongated direction, by the blade edge portions 412, 414. As the material 50, 52 separates, it curls or rolls inward of the diffuser 12, away from the point of contact to define first and second flash portions 54, 56. The flash portions 54, 56 that are cut from the side wall 22 to form the slots or openings 40 remain connected to and intact with the side wall 22 of the diffuser 12, at an interior of the side wall 22, so that the flash portions 54, 56 do not create cutting debris. It has also been observed that the flash portions 54, 56 do not adversely effect the flow area across the openings 40 or the total flow through the diffuser 12. Advantageously, unlike drilled or punched openings, the lanced slots or openings 40 can be formed in the diffuser side wall 22 after the bottom wall 26 is formed. One benefit that is realized by this arrangement is that the diffuser 12 can be formed as a single, unitarily formed part. This reduces the overall cost of fabricating the diffuser 12 because less labour intensive processes are required. In addition, because the flash portions 54, 56 remain connected to the diffuser side wall 22, less post-formation operations are necessary to finish the part for subsequent assembly of the restraint system. As seen in FIG. 7, the lance blades 410 (two shown) are mounted to a lancing apparatus 418 that includes a standard 420 for supporting the diffuser 12 during the lancing operation. The lance blades 410 can be equally circumferentially spaced from adjacent lance blades 410 by any variation of angles to form the desired slot 40 arrangement. That is, the diffuser 12 can be positioned much like the hub of a wheel, with the blades 410 positioned as wheel spokes at any of a variety of angles relative to one another. In the arrangement, the blades 410 can contact and pierce the diffuser 12, to form the slots or openings 40 simultaneously, so as to apply substantially equal force on the diffuser 12 from the various locations therearound during the piercing process.

Claims: A diffuser (12) for a supplemental restraint system including an airbag and a combustion chamber for providing a pressurized gas to inflate the air bag, the diffuser comprising: a substantially cylindrical member having a top wall (24), a cylindrical side wall (22) and a bottom wall (26) defining a diffuser chamber and defining a longitudinal axis, the bottom wall (26) having an opening (28) therein of predetermined flow area for communicating with the combustion chamber (14); and a plurality of elongated, through-wall slots (40) formed in the cylindrical side wall (22), extending generally parallel to the diffuser axis; characterised in that the slots (40) are formed by lancing. A diffuser in accordance with claim 1, wherein the slots (40) are configured and have a total flow area that is at least equal to the diffuser bottom wall opening (28) flow area to rapidly inflate the airbag. A diffuser in accordance with any one of the preceding claims, wherein the slots (40) have a generally rectangular shape. A diffuser in accordance with claim 3, wherein each slot (40) has a height extending parallel to the axis of about 5mm (0.20in) and a width of between about 0.75mm and 1mm (0.03 and 0.04in) to retain debris generated from the combustion chamber within the diffuser, and to prevent the debris from entering the airbag upon inflation such that a screen element is not required either within the diffuser or between the diffuser and the combustion chamber. A diffuser in accordance with any one of the preceding claims, including sixteen slots (40), wherein the slots (40) have a total flow area of between about 60mm 2 and about 80mm 2 (0.096 and 0.128in 2 ). A diffuser in accordance with any one of the preceding claims, wherein each slot (40) is formed so as to form at least one flash portion and wherein the at least one flash portion remains intact with the diffuser cylindrical side wall (22) upon formation. A diffuser in accordance with any one of the preceding claims, wherein each slot (40) is formed so as to define first and second flash portions (54,56) extending from opposing ends of the slots (40), and wherein the flash portions (54,56) remain intact with the diffuser cylindrical side wall (22) upon formation. A combustion chamber/diffuser combination comprising a diffuser in accordance with any one of the preceding claims, attached to the open end of a combustion chamber (14) with communication between the combustion chamber (16) and the opening (28) blocked with a burst disk (34).

Inventors: SCHOENBORN RANDALL J, SCHOENBORN, RANDALL J.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1999
Main classification: B60R21
IPC codes: B60R21