Liquid propellant airbag inflator with dual telescoping pistons

• US 6,039,347 A
• Filed: 12/19/1997
• Issued: 03/21/2000
• Est. Priority Date: 02/03/1997
• Status: Expired due to Term

• Current Assignee: General Dynamics OTS Incorporated (General Dynamics Corporation)
• Original Assignee: General Dynamics Armament Systems, Inc. (General Dynamics Corporation)
• Inventors: Maynard, Alfred Charles
• Primary Examiner(s): Mai, Lanna
• Assistant Examiner(s): Ririe, Andrew J.
• Application Number:
  US08/994,135
• Time in Patent Office: 823 Days
• Field of Search: 280/741, 280/737, 280/742, 280/736
• US Class Current: 280/736
• CPC Class Codes: B60R 2021/2636 The volume of gas being continuously adjustable
• CPC Class Codes: B60R 21/264 using instantaneous generation of gas, e.g. pyrotechnic B60R21/268 takes precedence

Abstract

An airbag inflator includes a pair of telescoping pistons slidingly mounted within a housing. Pressurization of a combustion chamber by a pyrotechnic initiator acts on one piston to pressurize a hydraulic fluid chamber, which, in turn, acts on the other piston to pressurize a liquid propellant reservoir. Liquid propellant can then be regeneratively pumped from the reservoir into the combustion chamber for combustion to generate an airbag inflation gas. A hydraulic fluid damping chamber is utilized to exert a controllable retarding force on the one piston, such as to control the rate of airbag inflation gas generation.

Claims

1. An airbag inflator comprising:

a housing;

first and second pistons in telescoping relation to one another and mounted for axial sliding motion within the housing;

a combustion chamber within the housing;

a reservoir within the housing containing a liquid propellant;

an injection orifice, through which the liquid propellant may flow from the reservoir into the combustion chamber;

a coupling chamber within the housing containing a hydraulic fluid exposed to the first and second pistons; and

a pyrotechnic initiator within the housing operable to pressurize the combustion chamber, the combustion chamber pressure exerting a force tending to drive the first piston in a first axial direction to pressurize the coupling chamber hydraulic fluid, and the pressurized coupling chamber hydraulic fluid exerting a force tending to drive the second piston in a second axial direction opposite the first axial direction to pressurize the liquid propellant in the reservoir, the liquid propellant pressure exceeding the combustion chamber pressure, such that the liquid propellant may be regeneratively pumped through the injection orifice into the combustion chamber for combustion to produce airbag inflation gas.

2. The airbag inflator of claim 1, further comprising a damping chamber within the housing chamber containing a hydraulic fluid exposed to the first piston, motion of the first piston in the first axial direction pressurizing the damping chamber hydraulic fluid, such as to exert a retarding force on the first piston affecting a rate of the motion in the first axial direction.

3. The airbag inflator of claim 2, wherein the damping chamber hydraulic fluid is a magnetorheological hydraulic fluid, the airbag inflator further comprising an electromagnet for generating a magnetic field in a gap through which the magnetorheological hydraulic fluid flows from the damping chamber while pressurized by the motion of the first piston in the first axial direction, variations in the magnetic field varying the viscosity of the magnetorheological fluid to produce corresponding variations in the retarding force.

4. The airbag inflator of claim 3, wherein the second piston is telescopically received within the first piston.

5. The airbag inflator of claim 4, wherein the liquid propellant reservoir is defined between the first piston and a front face of the second piston.

6. The airbag inflator of claim 5, wherein the coupling chamber is defined between rear faces of the first and second pistons and a rear section of the housing.

7. The airbag inflator defined in claim 6, wherein the injection orifice is included in a front face of the first piston.

8. The airbag inflator defined in claim 7, wherein the housing includes a first bore in a forward section thereof and a second bore in the rear section thereof, the first bore having a larger diameter than the second bore, and wherein the first piston comprises a head slidingly received in the first bore and including the front face, and a conjoined cylindrical skirt, slidingly received in the second bore and having a free end including the rear face, the second piston slidingly received within the cylindrical skirt.

9. The airbag inflator of claim 8, wherein the initiator is mounted in a forward end of the housing and includes a solid propellant-containing tube having an apertured terminal portion projecting into the combustion chamber.

10. The airbag inflator of claim 9, further comprising baffles positioned in the forward housing section, at least one of the baffles positioned in confronting relation with the first piston front face to define a boundary of the combustion chamber, the one baffle including pressure-frangible ports that open to permit escape of airbag inflation gas when the combustion chamber pressure exceeds a threshold pressure, the escaping airbag inflation gas flowing through openings in another of the baffles leading to an exhaust port in the housing.

11. The airbag inflator of claim 8, further comprising a compression spring positioned to exert a force on the first piston in the first axial direction.

12. The airbag inflator of claim 8, further comprising a bowed leaf spring disposed against a concave groove surface provided in the second piston rear face, opposed end portions of the leaf spring engaged in notches provided in the first piston skirt.

13. The airbag inflator of claim 8, further comprising a protuberance mounted to the second piston rear face for projection through the coupling chamber into contact with an endwall of the rear housing section.

14. The airbag inflator of claim 8, further comprising an encapsulation liner including a cylindrical wall covering an interior surface of the first piston cylindrical skirt and a radial wall covering the first piston front face, the liner radial wall including a pressure frangible section normally blocking the injection orifice in the first piston front face.

15. The airbag inflator of claim 14, wherein the first piston front face includes an orifice plate having a radial wall section surrounding a central well projecting into the combustion chamber and a plurality of injection orifices, and the liner radial wall including a radial wall section lying against the orifice plate radial wall section and an outstanding post joined to the liner radial wall section by the pressure frangible section and projecting partially into the well, upon rupture of the pressure frangible section due to pressurization of the liquid propellant in the reservoir, the post being freed to move further into the well, such as to expose the injection orifices for injection therethrough of the liquid propellant into the combustion chamber.

16. The airbag inflator of claim 15, wherein the post is equipped with an O-ring seal to provide a fluid seal with an entry portion of an interior surface of the well.

17. The airbag inflator of claim 16, wherein a bottom portion of the well interior surface is recessed to allow trapped air to escape past the O-ring seal.

18. The airbag inflator defined in claim 17, wherein the injection orifices are drilled through a sidewall of the well to provide open ends at the entry portion of the well interior surface, the post being sized to block the injection orifice open ends prior to rupture of the pressure frangible section, the airbag inflator further comprising a spring positioned in the well to bias the freed post back toward the entry portion of the well interior surface, such as to block the injection orifice open ends should the liquid propellant pressure in the reservoir fall to a low level.

19. The airbag inflator of claim 8, wherein the damping chamber is an annular chamber defined between the first housing bore and the first piston skirt.

20. The airbag inflator of claim 19, further comprising an accumulator chamber in fluid flow communication with the damping chamber through at least one port, the electromagnet positioned in the accumulator chamber.

21. The airbag inflator of claim 20, further comprising an absorbent material member positioned in the accumulative chamber.

22. The airbag inflator of claim 20, further comprising a jacket fixed to the housing to provide the accumulator chamber as an annular chamber surrounding the rear section of the housing.

23. The airbag inflator of claim 22, wherein the electromagnet includes an annular core surrounding the rear housing section and positioned to define an annular gap with one of the rear housing section and the jacket, the magnetorheological hydraulic fluid flowing from the at least one port provided in the housing through the gap.

24. The airbag inflator of claim 2, wherein the housing includes a first bore in a forward section thereof and a second bore in a rear section thereof, the first bore having a larger diameter than the second bore, the first piston comprising a head slidingly received in the first bore and a conjoined cylindrical skirt slidingly received in the second bore, the damping chamber being defined between a peripheral surface of the skirt and the first housing bore, the airbag inflator further comprising a port in the rear housing section having an open end exposed in the second bore, the port open end normally blocked by a terminal portion of the skirt peripheral surface, and an elongated groove of varying width and/or depth formed in the skirt peripheral surface to extend from the port blocking terminal portion of the skirt peripheral surface in the second axial direction toward the first piston head, whereby, upon movement of the first piston in the first axial direction, the port open end is exposed by the groove to permit a rate of hydraulic fluid flow from the damping chamber to varying as a function of first piston displacement and to produce corresponding variations in the retarding force.

25. The airbag inflator of claim 24, wherein a plurality of angularly spaced elongated grooves are formed in the skirt peripheral surface, the airbag inflator further comprising an annular groove formed in the second housing bore to expose the port open end, the terminal portion of the skirt peripheral surface normally blocking the annular groove.