Air bag module with variable inflation

The present invention relates generally to vehicle supplemental inflatable restraint systems and, more particularly, to an air bag module that provides variable output inflation of an air bag cushion from a single inflator. Variable deployment performance by controlling the quantity and fluid flow path of the inflator gas into or out of an air bag module according to the present invention. The air bag module includes a vent opening and a cushion retainer diffuser including a plurality of diffuser openings which permits fluid communication between an annular cavity and an air bag cushion. The vent opening provides a fluid path for the inflator gas to flow from the annular cavity to outside of the air bag module. For full level deployment, the vent opening is closed and therefore the inflator gas is not permitted to flow away from the air bag module but instead flows into the air bag cushion. For low level deployment, the volume of inflator gas which flows into the air bag cushion is controlled by selecting the ratio between the cross-sectional area of the diffuser openings and the cross-sectional area of the vent opening. For example, for reduced low level deployment, the cross-sectional area of the vent opening is increased in relation to the cross-sectional area of the diffuser openings. Conversely, for increased low level deployment, the cross-sectional area of the vent opening is decreased in relation to the cross-sectional area of the diffuser openings. Accordingly, the selective control of the ratio acts as a tuning mechanism by which different low level inflator outputs can be achieved. Deployment module levels between low level and high level can be achieved by controlling the timing of when the vent opening is closed.