Varying permeability filter for airbag inflator

Abstract

A new and improved airbag inflator including a varying permeability filter. The inflator includes a housing for holding gas generating materials and has an outer diffuser wall with a plurality of discharge or diffuser ports arranged to direct the gas into an airbag for rapid inflation. The housing includes a ring of diffuser ports spaced apart around the periphery of the outer diffuser side wall and these ports are generally closer to one of the top or bottom end walls of the container than they are to the opposite end wall. A new and improved gas filter of varying permeability is mounted in the housing inside the periphery of the outer diffuser wall adjacent to the ring of ports. The annular filter has a gas permeability characteristic that varies between a maximum permeability rating in a first region farthest away from the ring of ports to a minimum permeability rating adjacent a second region closer to the ports. The varying permeability areas tend to equalize or even out the gas flow over the entire available flow cross-section of the filter so that blow-through or burn holes do not develop. Moreover, the more uniform and even flow through the entire available flow cross-section results in a maximum of filtering and entrapment of contaminants as well as excellent cooling of the hot gases with the least flow resistance overall to provide rapid inflation of the airbag during deployment.