Pyrotechnic mixture and gas generator for an airbag

• US 5,589,662 A
• Filed: 06/07/1995
• Issued: 12/31/1996
• Est. Priority Date: 09/21/1992
• Status: Expired due to Fees

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Schwarz, Wolfgang, Feuerstake, Eugen, Klober, Martin, Schleicher, Ulrich
• Primary Examiner(s): Jordan, Charles T.
• Assistant Examiner(s): CHI, ANTHONY
• Application Number:
  US08/475,673
• Time in Patent Office: 573 Days
• Field of Search: 264/3.4, 149/36, 149/35
• US Class Current: 149/35
• CPC Class Codes: B60R 21/2644 using only solid reacting substances, e.g. pellets, powder
• CPC Class Codes: C06B 21/0066 by granulation, e.g. flaking
• CPC Class Codes: C06B 21/0083 Treatment of solid structures, e.g. for coating or impregnating with a modifier compositions therefor C06B23/00
• CPC Class Codes: C06B 35/00 Compositions containing a metal azide
• CPC Class Codes: C06D 5/06 by reaction of two or more solids
• CPC Class Codes: Y10S 149/11 Particle size of a component

Abstract

A pyrotechnic mixture in the form of granulates, encompassing a nitrogen-generating substance, an inorganic oxidizing medium and a binder constituted of silicone rubber. Also disclosed is a process for the production of this pyrotechnic mixture, as well as a gas generator for an airbag which contains the pyrotechnic mixture as a propellent charge. The pyrotechnic mixture is in the form of granulates for a propellent charge which generates a non-toxic gas, encompassing the nitrogen-generating substance, especially an alkali metal azide or earth alkali metal azide, an inorganic oxidizing medium consisting of alkali metal nitrate and/or alkaline earth metal nitrate and silicone rubber.

Claims

1. Gas-generator, particularly for an airbag, comprising as a propellant charge a pyrotechnic mixture in the form of granulates comprising a nitrogen-generating substance, an inorganic oxidizing agent and as a binder silicone rubber, wherein said nitrogen-generating substance is an alkaline metal azide, an alkaline earth metal azide or an ammonium azide, characterized in that said mixture contains granulates each comprising a plurality of particles of the nitrogen-generating substance and the inorganic oxidizing agent having a size of from 1 μ

m to 200μ

m, which are bonded together by said binder, which is present in an amount of 13 to 28%, based on the weight of the total mixture.

2. Gas-generator for an airbag according to claim 1, characterized in that the pyrotechnic mixture (3) is present in an amount of 0.05 to 0.7 g per liter of the gas volume which is to be produced by the generator during the inflation of the airbag by the ignited propellant charge under an ambient pressure.

3. Gas-generator according to claim 1, characterized in that it contains a container (2) having a plurality of discharge openings (2 ) , in which the pyrotechnical mixture (3) and at least one ignition element (13, 14) are provided.

4. Gas-generator according to claim 3, characterized in that the container (2) is surrounded by a space (29) at least in the area of the openings (20), which is delimited by a gas-permeable separator (23, 24, 25) from the airbag volume (31).

5. Gas-generator according to claim 3, characterized in that the container (2) is surrounded by a space (29) at least in the area of the openings, which is formed in such a way that during the inflation of the airbag by the ignited propellant charge a higher pressure exists in the space (29) than in the airbag volume (31).

6. Gas-generator according to claim 3, characterized in that during the inflation of the airbag a pressure exists in the inner space of the container (2), which is more than the factor 2 higher than the pressure which exists outside the container (2).

7. Gas-generator according to claim 3, characterized in that the container (2) is formed essentially cylindrical and comprises a plurality of openings (20) at its periphery.

8. Gas-generator according to claim 3, characterized in that the container (2) comprises a surrounding wall (32) having a wall thickness of from 0.5 to 10 mm and the material of the container is selected from the group of metals consisting of aluminum and stainless steel, or a ceramic material consisting of a silicate.

9. Gas-generator according to claim 8, characterized in that the space (29) is defined by the surrounding wall (32) of the container (2) and a separator (23, 24, 25), wherein said separator is impermeable for solid particles leaving the container and having a diameter of at least 0.3 mm which are produced by the burning of the propellant charge.

10. Gas-generator according to claim 9, characterized in that the distance of the separator (23, 24, 25) from the surrounding wall (32) of the container (2) at least in the area of the openings is such that a discharge of the gas which is produced during the burning of the propellant charge through the openings (20) of the container (2) takes place at sonic velocity.

11. Gas-generator according to claim 10, characterized in that the distance of the separator (23, 24, 25) from the surrounding wall of the container is 3.5 to 5 mm at least in the area of the openings.

12. Gas-generator according to claim 9, characterized in that the separator comprises at least an inner separator element (23) and an outer separator element (24).

13. Gas-generator according to claim 12, characterized in that the separator elements comprise at least one inner metal mesh (23) having a mesh width of from 0.4 to 1 mm and at least one outer mesh (24) having a mesh width of 0.1 to 0.3 mm.

14. Gas-generator according to claim 13, characterized in that the inner metal mesh (23) has a wire thickness of from 0.05 to 0.5 mm and the outer metal mesh (24) has a wire thickness of from 0.05 to 0.3 mm.

15. Gas-generator according to claim 12, characterized in that a filter (25) of heat resistant material is provided between the inner separator element (23) and the outer separator element (24).

16. Gas-generator according to claim 9, characterized in that spacer elements (30) of heat insulating material are provided, which protect an airbag envelope (7) from contact with the container (2) and the separator (23, 24, 25) during the inflation.

17. Gas-generator according to claim 3, characterized in that the pyrotechnic mixture (3) in the container (2) is present in a loosely poured form.

18. Gas-generator according to claim 3, characterized in that the pyrotechnic mixture (3) in the container (2) is protected by a sealing element (10, 28), particularly a plastic or metal film, from contact with the atmosphere.

20. Gas generator according to claim 1 or 19 characterized in that said pyrotechnic mixture contains granulates each comprising a plurality of pregranulated products having a grain size of from 20 μ

m to 5 mm, which are bonded together by an additional binder.

19. Gas generator, particularly for an airbag, comprising as a propellant charge a pyrotechnic mixture in the form of granulates which comprise a nitrogen-generating substance, an inorganic oxidizing agent consisting of an alkaline metal nitrate and/or an alkaline earth metal nitrate, and silicone rubber, wherein said nitrogen-generating substance is an alkaline metal azide or an alkaline earth metal azide, characterized in that the azide portion amounts to 35 to 65 percent by weight, the nitrate portion to 20 to 45 percent by weight and the silicone rubber portion amounts to 13 to 28 percent by weight, the azide and nitrate in the granule exhibiting a grain size of 1 to 200 μ

m and the granule having a bulk density of 0.35 to 1.2 g/cm³.

21. Gas generator, particularly for an airbag, comprising as a propellant charge a pyrotechnic mixture in the form of granulates prepared by the steps of:

(a) providing particles of a nitrogen-generating substance and of an inorganic oxidizing agent having a particle size of from 1 μ

m to 200 μ

m, wherein said nitrogen-generating substance is an alkaline metal azide, alkaline earth metal azide or ammonium azide,

(b) mixing the particles from (a) with liquid silicone rubber wherein the amount of the silicone rubber is 13 to 28% based on the weight of the total mixture,

(c) producing granulates from the materials mixed according to step (b) having a grain size of 200 μ

m to 12 mm, and

(d) curing the granulates.

22. Gas-generator according to claim 21 wherein a hardener is additionally added in mixing step (b).

23. Gas-generator, particularly for an airbag, comprising as a propellant charge a pyrotechnic mixture in the form of granulates prepared by the steps of:

(a) providing particles of a nitrogen-generating substance and of an inorganic oxidizing agent having a particle size of from 1 μ

m to 200 μ

m, wherein said nitrogen-generating substance is an alkaline metal azide, alkaline earth metal azide or an ammonium azide,

(b) mixing the particles from (a) with a binder,

(c) producing pre-granulation products from the materials mixed according to step (b) having a grain size of from 20 μ

m to 5 mm,

(d) mixing the pregranulation products from (c) with liquid silicone rubber, wherein the amount of the silicone rubber is 13 to 28% based on the weight of the total mixture,

(e) producing granulates from the materials mixed according to step (d) having a grain size of from 200 μ

m to 12 mm, and

(f) curing the granulates.

24. Gas-generator according to claim 23 wherein a solvent or suspending agent is additionally employed in step (b).

25. Gas-generator according to claim 23 wherein a hardener is additionally added in mixing step (d).