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The variable output inflator includes an injection piston assembly containing a liquid propellant chamber from which liquid propellant is injected through one or more nozzles in the injection piston into a combustion chamber. The movement of the injection piston is controlled by a magnetic control u

The variable output inflator includes an injection piston assembly containing a liquid propellant chamber from which liquid propellant is injected through one or more nozzles in the injection piston into a combustion chamber. The movement of the injection piston is controlled by a magnetic control unit employing an annular gap through which the MR fluid flows in a controlled manner. The inflator is of cylindrical type and may be made of small compact dimensions.

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1. A variable output inflator comprisinga housing having a combustion chamber therein and at least one port for expelling combustion gas from said combustion chamber; an initiator mounted on said housing for introducing a combustion gas into said combustion chamber; an injection piston slidably moun

1. A variable output inflator comprisinga housing having a combustion chamber therein and at least one port for expelling combustion gas from said combustion chamber; an initiator mounted on said housing for introducing a combustion gas into said combustion chamber; an injection piston slidably mounted in said combustion chamber of said housing for movement between an initial position and a second position in response to the introduction of a combustion gas into said combustion chamber from said initiator, said piston including a propellant chamber therein for containing a charge of liquid propellant therein and means communicating said propellant chamber with said combustion chamber to deliver liquid propellant thereto; and a magnetic control unit for controlling movement of said injection piston from said first position to said second position, said magnetic control unit including a sleeve within said housing coaxially of said injection piston to define a third chamber therebetween for receiving a magneto-rheological fluid, a core disposed in and concentrically spaced from said sleeve to define a gap therebetween communicating with said third chamber, and at least one electromagnetic coil for producing an electromagnetic field across said gap to affect the rheological properties of the magneto-rheological fluid in said gap whereby an increase in the electromagnetic field effects an increase in the flow resistance of the magneto-rheological fluid in said gap to slow the movement of said injection piston. 2. An inflator as set forth in claim 1 wherein said sleeve and said core define a gap of decreasing thickness in a direction away from said third chamber.3. An inflator as set forth in claim 1 comprising a pair of said electromagnetic coils disposed in spaced apart relation along said gap to produce a different electromagnetic field across said gap.4. A variable output inflator comprisinga housing having a combustion chamber therein and at least one port for expelling combustion gas from said combustion chamber; an initiator mounted on said housing for introducing a combustion gas into said combustion chamber; an injection piston slidably mounted in said combustion chamber of said housing for movement between an initial position and an expelled position in response to the introduction of a combustion gas into said combustion chamber from said initiator, said piston including a propellant chamber therein for containing a charge of liquid propellant therein, at least one nozzle communicating said propellant chamber with said combustion chamber to deliver liquid propellant thereto, and means for releaseably closing said nozzle to prevent communication between said propellant chamber and said combustion chamber; a plug mounted in said housing coaxially of said piston to slidably receive said piston; and a magnetic control unit for controlling movement of said injection piston relative to said plug. 5. A inflator as set forth in claim 4 wherein said magnetic control unit includes a sleeve within said housing coaxially of said injection piston to define a third chamber therebetween for receiving a magneto-rheological fluid, a core disposed in and concentrically spaced from said sleeve to define a gap therebetween communicating with said third chamber, and at least one electromagnetic coil for producing an electromagnetic field across said gap to affect the rheological properties of the magneto-rheological fluid in said gap whereby an increase in the electromagnetic field effects an increase in the flow resistance of the magneto-rheological fluid in said gap to slow the movement of said injection piston.6. A inflator as set forth in claim 5 wherein said core has an internal bore and a plurality of grooves in one end thereof communicating said gap with said bore to convey the magneto-rheological fluid from said third chamber to said bore in response to movement of said injection piston over said plug.7. A inflator as set forth in claim 6 which further comprises a closure plate within said housing abutting said sleeve and said core at one end thereof, and a piston slidably mounted in said bore for movement from a first position adjacent said closure plate to a position remote from said closure plate in response to the magneto-rheological fluid filling said bore.8. An inflator as set forth in claim 4 wherein said means for releaseably closing said nozzle includes a tape secured to said injection piston over said nozzle on a side facing said combustion chamber to prevent a flow of combustion gas from said combustion chamber through said nozzle during startup.9. An inflator as set forth in claim 8 wherein said tape is a metal tape.10. An inflator as set forth in claim 9 wherein said tape is made of aluminum.11. An inflator as set forth in claim 8 wherein said means for releaseably closing said nozzle further includes a plug fitted into said nozzle, said plug being expellable from said nozzle into said combustion chamber in response to a pressurized flow of liquid propellant from said propellant chamber.12. An inflator as set forth in claim 11 wherein said plug in said nozzle is made of Nylon.13. An inflator as set forth in claim 4 wherein said injection piston is made of metal and which further comprises a coating on said injection piston within said propellant chamber to prevent contact between a liquid propellant in said propellant chamber and said metal piston.14. An inflator as set forth in claim 13 wherein said coating is made of a polytetrafluoroethylene plastic.15. An inflator as set forth in claim 4 wherein said injection piston has a nose projecting into said combustion chamber and having a conically shaped section and wherein said nozzle has an outlet located in said conically shaped section.16. An inflator as set forth in claim 15 wherein injection piston has a plurality of said nozzles in said conically shaped section and said means includes a conically shaped tape secured to said conically shaped section over said nozzles.17. An inflator as set forth in claim 15 which further comprises an injection plug slidably mounted in said nose to move from a first position blocking communication between said propellant chamber and said nozzle to a second position to permit communication between said propellant chamber and said nozzle in response to a pressurized flow of liquid propellant from said propellant chamber.18. An inflator as set forth in claim 4 wherein said injection piston has a circumferential skirt defining said propellant chamber and further comprising a pump piston mounted in abutment with one end of said plug and slidably receiving said skirt of said injection piston thereon.19. An inflator comprisinga cylindrical housing having a combustion chamber therein and at least one exhaust port for expelling combustion gas from said combustion chamber; an initiator mounted on one end of said housing for introducing a combustion gas into said combustion chamber; an injection piston slidably mounted in said combustion chamber of said housing for movement between an initial position and an expelled position in response to the introduction of a combustion gas into said combustion chamber from said initiator, said piston including a propellant chamber therein for containing a charge of liquid propellant therein, at least one nozzle communicating said propellant chamber with said combustion chamber to deliver liquid propellant thereto, and means for releaseably closing said nozzle to prevent communication between said propellant chamber and said combustion chamber; a plug mounted in said housing on an opposite side of said injection piston from said initiator and coaxially of said piston to slidably receive said piston; and a magnetic control unit for controlling movement of said injection piston relative to said plug. 20. An inflator as set forth in claim 19 wherein said magnetic control unit includes a sleeve within said housing coaxially of said injection piston to define a third chamber therebetween for receiving a magneto-rheological fluid, a core disposed in and concentrically spaced from said sleeve to define a gap therebetween communicating with said third chamber, and at least one electromagnetic coil for producing an electromagnetic field across said gap to affect the rheological properties of the magneto-rheological fluid in said gap whereby an increase in the electromagnetic field effects an increase in the flow resistance of the magneto-rheological fluid in said gap to slow the movement of said injection piston.21. An inflator as set forth in claim 20 wherein said core has an internal bore and a plurality of grooves in one end thereof communicating said gap with said bore to convey the magneto-rheological fluid from said third chamber to said bore in response to movement of said injection piston over said plug.22. An inflator as set forth in claim 19 wherein said means includes a tape secured to said injection piston over said nozzle on a side facing said combustion chamber to prevent a flow of combustion gas from said combustion chamber through said nozzle during startup.23. An inflator as set forth in claim 22 wherein said means further includes a plug fitted into said nozzle, said plug being expellable from said nozzle into said combustion chamber in response to a pressurized flow of liquid propellant from said propellant chamber.24. An inflator as set forth in claim 19 wherein said injection piston is made of metal and which further comprises a coating on said injection piston within said propellant chamber to prevent contact between a liquid propellant in said propellant chamber and said metal piston.25. An inflator as set forth in claim 19 wherein said injection piston has a nose projecting into said combustion chamber and having a conically shaped section and wherein said nozzle has an outlet located in said conically shaped section.26. An inflator as set forth in claim 25 wherein injection piston has a plurality of said nozzles in said conically shaped section and said means includes a conically shaped tape secured to said conically shaped section over said nozzles.27. An inflator as set forth in claim 25 which further comprises an injection plug slidably mounted in said nose to move from a first position blocking communication between said propellant chamber and said nozzle to a second position to permit communication between said propellant chamber and said nozzle in response to a pressurized flow of liquid propellant from said propellant chamber.28. An inflator as set forth in claim 19 further comprising a second piston mounted in abutment with one end of said plug and slidably receiving said injection piston thereon to pressurize liquid propellant in said propellant chamber in response to sliding of said injection piston onto said second piston.29. An inflator as set forth in claim 28 wherein said second piston is made of plastic.30. An inflator comprisinga cylindrical housing having a combustion chamber therein and at least one exhaust port for expelling combustion gas from said combustion chamber; an initiator mounted on one end of said housing for introducing a combustion gas into said combustion chamber; an injection piston slidably mounted in said combustion chamber of said housing for movement between an initial position and an expelled position in response to the introduction of a combustion gas into said combustion chamber from said initiator, said piston including a propellant chamber therein for containing a charge of liquid propellant therein, at least one nozzle communicating said propellant chamber with said combustion chamber to deliver liquid propellant thereto, and means for releaseably closing said nozzle to prevent communication between said propellant chamber and said combustion chamber; a plug mounted in said housing on an opposite side of said injection piston from said initiator and coaxially of said piston in spaced relation to said housing to define a chamber for receiving a magneto-rheological fluid and to slidably receive said piston; and a magnetic control unit for affecting the rheological properties of the fluid in said chamber to control the movement of said injection piston relative to said plug into said chamber.