Two-stage automotive gas bag inflator using igniter material to delay

Abstract

A dual-stage gas bag inflator, operable initially, when activated, to cause the gas bag to deploy slowly and then, after a delay, to deploy rapidly, includes a housing having first and second compartments of different size separated by a bulkhead. The first compartment is the smaller since it is to produce a smaller amount of gas to cause the initial slow deployment of the gas bag. A gas generant charge is ignited in the first compartment, and after some delay, a gas generant charge in the second compartment is ignited. The delay is produced by an initiator including a squib, igniter material in each of the first and second compartments, and a fuse cord which is ignited by the squib. The fuse cord passes through the bulkhead and ignites all igniter materials in both inflator compartments simultaneously. The igniter material in the second compartment is so characterized that it burns slower than the igniter material in the first compartment. When ignited, the igniter material in the first compartment burns outwardly rapidly while that in the second compartment burns outwardly relatively slower. As a result, the gas generant in the first compartment is ignited before the gas generant in the second compartment. The burn rate of the igniter material in the second compartment may be made slower than that in the first compartment by using igniter materials of different chemical composition or by increasing the size of the igniter material, giving it a greater burn area, thus causing it to be consumed slower.