Inflator

1. A cylindrical inflator comprises:

an elongated tubular housing having a first end sealed by an igniter assembly and an opposite second end sealed by a diffuser assembly, the diffuser assembly having a first set of discharge openings sealed by frangible foil, and a combustion chamber interposed and extending between the igniter assembly and the foil sealed diffuser assembly;

a hollow tubular filter positioned inside the combustion chamber having an enlarged first end compressed against an inner wall of the elongated tubular housing and an elongated narrow portion extending from the enlarged first end of the hollow tubular filter toward the second end of the tubular housing having an end attached to or abutting an internal end of the diffuser assembly, the elongated narrow portion being spaced from the elongated tubular housing to form a gas discharge plenum;

a plurality of gas generant pellets at least partially filling the combustion chamber;

a compressible spring having a first end and a second end, the first end of the spring abutting the enlarged first end of the hollow tubular filter; and

a filter abutting the second end of the compressible spring,

wherein upon ignition, the gas generant pellets generate inflation gases under pressure to enter and pass through the narrow portion of the hollow tubular filter filling the gas discharge plenum and bursting the foil opening the discharge openings and passing out the diffuser assembly.

2. The inflator of claim 1 wherein the gas discharge plenum externally encircles the elongated narrow portion of the hollow tubular filter.

3. The inflator of claim 2 wherein the gas discharge plenum extends longitudinally between the enlarged first end of the hollow tubular filter to the second end of the elongated tubular housing.

4. The inflator of claim 3 wherein the inflation gases generate a pressure of the ignited gas generant pellets that applies a seal burst force directed radially inwardly toward a center axis of the inflator.

5. The inflator of claim 4 wherein the diffuser assembly has a second set of discharge openings positioned radially to direct gas flow radially outward.

6. The inflator of claim 1 wherein the elongated tubular housing has an outer diameter of 35 mm or less.

7. The inflator of claim 1 wherein the elongated tubular housing has a longitudinal length L H of 25 cm or less.

8. The inflator of claim 1 wherein the elongated tubular housing has a longitudinal length L H , wherein the hollow tubular filter extends inwardly a distance L F relative to the elongated tubular housing from the second end of the elongated tubular housing a distance less than half the elongated tubular housing longitudinal length L H .

9. The inflator of claim 1 wherein the inflator has a gas generant pellets fill volume defined by a length L H of the elongated tubular housing minus a combined length L F2 of the compressible spring and filter, the hollow tubular filter, and the diffuser assembly as measured from the second end of the elongated tubular housing.

10. The inflator of claim 9 wherein the compressible spring and filter move when a sufficient amount of gas generant pellets burn after ignition, such that the combined length L F2 of the compressible spring and filter, the hollow tubular filter, and the diffuser assembly as measured from the second end of the elongated tubular housing becomes a new length L F1 , wherein L F1 is less than L F2 .

11. The inflator of claim 1 wherein the compressible spring and filter provide a pushing force against the gas generant pellets prior to ignition.