Airbag inflator with external filter

This application claims the benefit of provisional application Ser. No. 60/150,049 filed on Aug. 20, 1999.

Installation of inflatable occupant restraint systems, generally known as “airbags”, as standard equipment in all new vehicles, has intensified the search for smaller, lighter, less expensive restraint systems. Accordingly, since the inflator used in such systems is the heaviest and most expensive component of an inflatable occupant restraint system, there is a need for a lighter and less expensive inflator.

A typical inflator comprises a cylindrical steel or aluminum housing having a diameter and length related to the vehicle application and characteristics of the propellant contained therein. The inflator is generally provided with an internal filter comprising one or more layers of steel screen of varying mesh and wire diameter. Gas produced upon combustion of the propellant passes through the filter before exiting the inflator. Co-owned U.S. Pat. Nos. 5,628,528 and 5,622,380, herein incorporated by reference, exemplify inflators having internal filters.

However, known internal filters are, of necessity, relatively heavy due to their disposition in close proximity to the propellant. The high gas temperatures produced upon combustion of the propellant dictate the use of relatively heavy wire mesh to preclude burn through. In addition, since it is desirable to maximize the pressure and volume of the gas entering the airbag in relation to the size of the inflator, pressure attenuation upon passage of combustion gases through the filter must be minimized.

The solution to the problem of reducing airbag inflator size, weight, cost and efficiency, in accordance with the present invention, is predicated on the concept that it is possible to utilize a relatively small and lightweight filter if it is disposed externally of the inflator housing and properly orientated relative to the gas discharge apertures in the inflator housing. Moreover, external orientation of the filter in spaced relation to the gas discharge orifice of the inflator effects expansion and cooling of combustion gases, minimizes heating of the filter and minimizes pressure drop in the gases emanating from the inflator.

FIG. 1 is an elevational view, partially in section, of a driver side inflator.

FIG. 2 is an enlarged view taken with the circle 2 of FIG. 1 .

As seen in FIG. 1 of the drawing, a driver side airbag module 10 , comprises four major components, namely, a housing 12 having a rupturable frontal closure 14 , an airbag 16 and an inflator 18 having a propellant 20 therein. The inflator 18 comprises upper and lower cup-shaped sections 21 and 22 , respectively, that are welded together in inverted nested relationship. The upper housing section 21 of the inflator 18 contains a plurality of apertures 24 for effecting radial discharge of gas produced by the propellant 20 . The inflator 18 has a perforated and centrally disposed igniter support tube 30 welded therein for the support of an igniter 32 . The perforated tube allows a frame front generated by the igniter 32 to pass to the propellant 20 , thereby igniting propellant 20 and producing an inflating gas. The propellant 20 may be any known gas generant composition useful for airbag application and is exemplified by, but not limited to, compositions described in U.S. Pat. No. 5,035,757 herein incorporated by reference.

In accordance with the present invention, at least one annular filter 40 is disposed externally of the inflator 18 . The filter 40 comprises a fine wire mesh annulus that is retained by a combination filter retainer, airbag anchor, and combustion gas deflector 42 . A lower end portion 44 of the airbag 16 is folded radially inwardly under a radial flange 46 on the filter retainer 42 . A radially inwardly extending flange 48 on the filter retainer 42 secures the filter 40 in radially spaced relation to the upper wall section 21 of the inflator 18 . The filter 40 is readily obtainable by sources well known in the art.

In accordance with one feature of the invention, the gas discharge apertures 24 in the upper section 21 of the inflator 18 are radially aligned with the filter 40 . The high-velocity gas exiting the inflator 18 is volumetrically expanded and cooled in an annular space 50 between the upper wall section 21 of the inflator 18 and the filter 40 , prior to entering the filter 40 . Thus, given a reduction in velocity, the filter 40 can be fabricated from relatively fine, lightweight wire minimizing weight and maximizing its capability to filter fine particulates from the gas stream.

In one embodiment, for example, lightweight wire is exemplified but not limited to strands measuring from five to ten thousandths of an inch ({fraction (5/1000)} to {fraction (10/1000)} inches) in diameter, or less. The lightweight wire is then meshed together by methods well known in the art. Stated another way, lightweight wire filters are simply filters containing wires having a smaller diameter than those normally used in internal filters. Mesh filters are readily obtainable from companies such as Wayne Wire Cloth of Hillman, Mich. The filters can also be formed, for example, from sintered steel wool, or from loose metal fibers heated just below their melting point and then held at that temperature until the loose fibers are fused together.

As illustrated by the arrows in FIG. 2, the flange 48 on the filter retainer 42 redirects radial flow of the gas from the inflator 18 to axial flow into the airbag 16 .

In operation, gases generated by the propellant 20 exit apertures 24 and are cooled as they traverse annular space 50 and then radially impinge upon external filter 40 . As the gases migrate through the filter, the retainer 42 routes the inflating gases into the airbag 16 . In contrast to state-of-the-art inflators having an internal filter, the pressure drop of the gas leaving the filter is minimized while yet providing adequate filtration and cooling of the gas.

It will be understood that the foregoing description of the preferred embodiment of the present invention is for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications, none of which departs from the scope of the present invention as defined in the appended claims.