Explosive and thermic compositions or charges – Containing inorganic nitrogen-oxygen salt – Ammonium nitrate
Reexamination Certificate
1998-07-21
2001-10-02
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Containing inorganic nitrogen-oxygen salt
Ammonium nitrate
C149S019100, C149S046000
Reexamination Certificate
active
06296724
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus comprising an inflatable vehicle occupant protection device and a gas generating composition for providing inflation gas for inflating the inflatable vehicle occupant protection device.
BACKGROUND OF THE INVENTION
An inflatable vehicle occupant protection device, such as an air bag, is inflated by inflation gas provided by an inflator. The inflator contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated to ignite the body of gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
Gas generating compositions which include an organic fuel and ammonium nitrate as an oxidizer potentially provide a substantially smoke-free inflation gas that is substantially free of toxic materials. The organic fuel and ammonium nitrate are usually in the form of powders which are formed into a body of gas generating material having a discrete shape.
Motor vehicles may remain in service for many years and are subject to temperature extremes. Components of motor vehicles such as inflatable vehicle occupant protection devices undergo rigorous testing including temperature cycling from about −40° C. to above 100° C. When exposed to such temperature changes, ammonium nitrate can undergo phase changes and corresponding volumetric changes. The volumetric changes of the ammonium nitrate can adversely affect the integrity of the body of gas generating material, in turn adversely affecting the performance characteristics of the gas generating material during combustion. Furthermore, compositions containing large amounts of ammonium nitrate are difficult to ignite and prone to extinguishment.
The phase stabilization of ammonium nitrate is known to minimize the volumetric changes in ammonium nitrate due to temperature changes. One common method of phase stabilization is to dope the ammonium nitrate with a metal salt, such as potassium nitrate, in order to incorporate a metal ion such as potassium into the crystal lattice of the ammonium nitrate. This method of phase stabilization is only effective where rigorous exclusion of moisture is observed.
The above disadvantages of using ammonium nitrate as an oxidizer in a gas generating composition for inflating an inflatable vehicle occupant protection device can be reduced by minimizing the amount of ammonium nitrate in the gas generating composition. Nonetheless, it is desirable to achieve essentially complete combustion of the carbon atoms in the organic fuel to carbon dioxide rather than incomplete combustion to carbon monoxide as well as complete combustion of the hydrogen atoms in the organic fuel to water.
One approach to minimizing the amount of ammonium nitrate is to carefully select a fuel with a favorable oxygen content. With most organic fuels, at least about 60% by weight of the ammonium nitrate oxidizer, whether pure or phase stabilized, and more often, up to about 85% or more is required.
U.S. Pat. No. 5,545,272 discloses a gas generating composition which consists essentially of about 45% to about 65% phase stabilized ammonium nitrate (PSAN) and about 35% to about 55% nitroguanidine (NQ). Selection of nitroguanidine is beneficial since it is not a salt. Fuels which are salts are prone to complex phase equilibria in the presence of ammonium nitrate. Many form eutectics which are low melting, making them unsuitable for automotive applications.
SUMMARY OF THE INVENTION
The present invention resides in an apparatus comprising an inflatable vehicle occupant protection device and a gas generating composition for providing inflation gas for inflating the inflatable vehicle occupant protection device. The gas generating composition comprises an oxidizer and an organic fuel. The oxidizer is phase stabilized ammonium nitrate (PSAN). The organic fuel is a mixture of nitroguanidine (NQ) and a supplemental, non-salt fuel selected from the group consisting of 3-nitro-1,2,4-triazole-5-one (NTO) and cyclotetramethylenetetranitramine (HMX). The gas generating composition preferably also comprises up to about 10% by weight of a binder.
Preferably, the gas generating composition is oxygen balanced for substantially complete combustion of carbon in the organic fuel to carbon dioxide and hydrogen in the organic fuel to water while minimizing the formation of oxides of nitrogen.
In one embodiment of the present invention the gas generating composition consists essentially of phase stabilized ammonium nitrate (PSAN), nitroguanidine (NQ), 3-nitro-1,2,4-triazole-5-one (NTO) and up to about 10% of a binder based on the weight of the gas generating composition. The nitroguanidine and 3-nitro-1,2,4-triazole-5-one are present in approximately equal weight proportions. The weight ratio of the organic fuel to phase stabilized ammonium nitrate is preferably about 45:55 for substantially complete combustion of carbon in the organic fuel to carbon dioxide and hydrogen in the organic fuel to water while minimizing the formation of oxides of nitrogen.
In a second embodiment of the present invention, the gas generating composition consists essentially of phase stabilized ammonium nitrate (PSAN), nitroguanidine (NQ), cyclotetramethylenetetranitramine (HMX) and up to about 10% of a binder based on the weight of the gas generating composition. The nitroguanidine and cyclotetramethylenetetranitramine are present in approximately equal weight proportions. The ratio of the organic fuel to phase stabilized ammonium nitrate is preferably about 45:55 for substantially complete combustion of carbon in the organic fuel to carbon dioxide and hydrogen in the organic fuel to water while minimizing the formation of oxides of nitrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features of the present invention will become apparent to those skilled in the art to which the present invention relates, from consideration of the following specification, with reference to the accompanying drawing which is a schematic illustration of an apparatus embodying the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to the FIGURE, an apparatus
12
embodying the present invention comprises an inflator
14
. The inflator
14
contains a gas generating material
16
and optionally a stored gas. The gas generating material
16
is ignited by an igniter
18
operatively associated with the gas generating material
16
. Electric leads
19
convey current to the igniter
18
from a sensor which is responsive to a collision. The apparatus
12
also comprises a vehicle occupant protection device
20
. A gas flow means
22
conveys gas, which is generated by combustion of the gas generating material
16
in the inflator
14
, to the vehicle occupant protection device
20
. It is further contemplated that one or more of these inflator components may be present in duplicate for optimal occupant protection.
A preferred vehicle occupant protection device
20
is an air bag which is inflatable to protect a vehicle occupant in the event of a collision. Other vehicle occupant protection devices which can be used in the present invention are inflatable seat belts, inflatable knee bolsters, inflatable air bags to operate knee bolsters, inflatable head liners, and/or inflatable side curtains.
The gas generating composition of the present invention comprises an oxidizer and an organic fuel.
The oxidizer is phase stabilized ammonium nitrate (PSAN). The weight percent of the phase stabilized ammonium nitrate in the gas generating composition is from about 53% to about 57%, based on the combined weight of the phase stabilized ammonium nitrate and the organic fuel. Preferably, the weight percent of the phase stabilized ammonium nitrate in the gas generating
Miller Edward A.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Inc.
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