FORM - 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
NON-TOXIC GAS PROPELLANT FOR IGNITER OF AIRBAG
INFLATOR SYSTEM
(a)TATA CONSULTANCY SERVICES LIMITED
an Indian Company of Nirmal Building, 9th Floor, Nariman Point, Mumbai - 400021,
Maharashtra, India; and
(b) INDIAN INSTITUTE OF SCIENCE
an Indian Organization, IISc, Bangalore - 560012,
Kamataka, India.
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to propellants used for igniting a reactive mixture for inflating an airbag inflator system for vehicles. Particularly, the present invention relates to non-toxic gas propellant used in igniter of an airbag inflator system for vehicles.
BACKGROUND OF THE INVENTION
Airbags are used in cars as supplementary restraint systems to protect passengers in case of high speed collision. To reduce the risk of collision it has been known to mount an inflatable restraint on the hub of the steering wheel or on the instrument panel in the passenger compartment to supplement seat belts in the event of a frontal crash. Inflators form a part of the system and help in producing and injecting gas into the airbag at the required pressure and mass flow rate. There are several types of inflators: one type of inflator includes a pyrotechnic material that explodes to produce the required gas for inflation; another type of inflator involves using stored high pressure gas to inflate the airbag.
The pyrotechnic igniter /squib/detonators play a very critical role in the performance of the airbag inflator system. It provides the curtail heat required to start the combustion reaction of the solid gas generating propellant mixture (or the gas mixture) in the inflator to generate the gas, which will intern inflate the nylon airbag.

Most of the inflators use a solid propellant based pyrotechnic chemical boosters in the igniter /squib to generate the required heat to ignite the reactive mixture.
Conventional propellant chemistry used in igniters/ squib for airbags or detonators are all solid propellant like boron potassium nitrate. The ingredients used in this solid propellant might be combination of toxic / highly reactive chemicals, blended in a sophisticated remote controlled manufacturing process to achieve the desired performance. Some of these chemicals are expensive/toxic/ unstable and pose risk to human beings, if they come in contact with the chemicals. Most of the gas generators used in automotive safety systems uses such solid propellant chemicals for generating hot gases that may create a serious health hazard.
For example, US patent US5 507891 having priority date of August 11, 1995 discloses non-self extinguishing propellant compositions for use in hybrid automotive air bag systems. The propellant compositions are based on a mixture of a crystalline nitramine propellant, an energetic or non-energetic binder and one or a combination of an oxidizing propellant and an energetic plasticizer, However, the non-self extinguishing propellant compositions as disclosed by US5507891 patent is comparatively unsafe.
US patent US 6,009,810 having priority date of July 8, 1998 discloses a plasticizer-free propellant for inflating passenger airbags in vehicles. The plasticizer-free propellant includes from about 78 to about 90 weight percent of cyclotrimethylenetrinitramine (RDX) and from about 10 to about 22 weight percent of a plasticizer-free polymer binder formed by curing a

mixture of a polyoctenamer and a polymer comprising an acrylate polymer or a methacrylate polymer having a glass transition temperature of -30.degree Celcius or lower and 0.01 to 5 weight percent based on the total amount of the monomers, of a crosslinking monomer having two or more double bonds of substantially the same reactivity in the molecule or one double bond and a crosslinking functional group such as an epoxide ring, a hydroxyl group, or a carbonyl group. However, the propellant as used in the US 6,009,810 patent is unstable and may pose risk to human beings.
US publication US20030145923 having priority date of March 13, 2000 discloses a propellant for gas generators, especially for lifesaving systems, The propellant contains one or several tetrazole derivative(s) or respectively one or several compounds from the groups of (A) cyanic acid derivatives and their salts, (B) triazine and triazine derivatives, (C) urea, its salts, derivatives, and compounds evolved therefrom and their salts, wherein the aforementioned compounds can also be present as mixtures; and an oxidizing agent from the group of peroxides of zinc, calcium, strontium or magnesium or such peroxides with nitrates of ammonium, sodium, potassium, magnesium, calcium and iron, wherein it is possible to add further gas generating components, coolants, reducing agents, catalysts and/or porosity-producing media. However, the propellant disclosed by US20030145923 publication is a solid propellant based chemical mixture may pose risk to human beings.
US publication US20060075681 having priority date of June 13, 2005 A discloses a pyrotechnic composition for use in safety arrangements for motor vehicles. The pyrotechnic composition has an auto-ignition temperature

between 140 and 180 degrees C. and contains hydroxybenzotriazole in an amount of about 25 to 95% by weight of the composition. However, the pyrotechnic composition disclosed by US20060075681 publication is adapted to be auto-ignited.
US patent US7380820 having priority date of June 23, 2005 discloses an inflator for inflating an inflatable -vehicle occupant protection device. The inflator includes a structure that defines a chamber and inflation fluid stored in the chamber. The inflation fluid includes in mixture a fuel gas, an oxidizer gas, and an inert gas mixture. The inflator also includes an actuator for initiating a combustion reaction between the fuel gas and the oxidizer gas. The inert gas mixture includes at least two different inert gases and has a composition selected to produce desired performance characteristics of the inflator. However, the inflation fluid of the inflator disclosed by US7380820 patent is comparatively expensive because of use of at least two different inert gases.
US publication US20020144759 having priority date of April 25, 2006 discloses a propellant used to inflate an airbag in vehicle safety systems comprising from about 70 weight percent to about 82 weight percent Cyclotrimethylenetrinitramine (RDX), from about 10 weight percent to about 15 weight percent of a polymer binder, from about 6 weight percent to about 9 weight percent of an inert plasticizer, from about 2 weight percent to about 4 weight percent of Hydroxypropyl Cellulose, from about 0.5 weight percent to about 1 weight percent of a polymeric processing aid; and, from about 0.3 weight percent to about 0.5 weight percent of a material that acts as a stabilizer and anti-oxidant. However, the propellant as used in the

US20020144759 publication is unstable and may pose risk to human beings. Further, the propellant as used in the US20020144759 publication is the gas generating propellant and not the igniter propellant.
Accordingly, there is a need for a gas propellant that is non-toxic. Further, there is a need for a gas propellant that is safe and does not create any health hazard and simple to manufacture. Furthermore, there is a need for a low cost gas propellant that is efficient for inflating an airbag of an airbag inflator system.
OBJECTS OF THE INVENTION
An object of the present invention is to provide an igniter propellant for inflating an airbag inflator that is non-toxic under both pre combustion and post combustion scenarios.
Another object of the present invention is to provide a propellant for igniting the pyrotechnic or fluid reactive mixture in the inflator for inflating an airbag that has high reaction rate.
Yet another object of the present invention is to provide an igniter propellant for inflating an airbag inflator that does not self ignite.
Still another object of the present invention is to provide an igniter propellant for igniting the reactive mixture in the inflator for inflating an airbag that is adapted to generate a comparatively large amount of heat per unit mass of gas mixture.

une more object of the present invention is to provide an igniter propellant for inflating an airbag inflator that has low cost.
Also, an object of the present invention is to provide an igniter propellant that is safe and does not create any health hazard.
Additionally, an object of the present invention is to provide an igniter propellant that is efficient for inflating an airbag inflator system.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided a non-toxic gas propellant for an airbag inflator system. The non-toxic gas propellant includes hydrogen gas in the range of 25 to 40% of the total volume of the gases mixture, oxygen in the range of 12 to 25% of the total volume of the gases mixture, and inert gas in the range of 35 to 62% of the total volume of the gases mixture. The mixture is compressed at a pressure of 10 to 25 bar.
In one embodiment of the present invention, the inert gas is nitrogen.
Typically, the oxygen gas and nitrogen gas are combined in air.
Typically, the hydrogen gas is in the range of 30 to 35%.
Preferably, the oxygen gas is in the range of 12 to 17%.
Furthermore, the nitrogen gas is in the range of 47 to 62%.

Additionally, in one embodiment of the present invention the non-toxic gas propellant includes 31% hydrogen gas, 54% nitrogen gas, and 15% oxygen
gas.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The invention will now be described in relation to the accompanying drawings in which,
Figure 1 illustrates a graphical representation of pressure rise Vs. time for different molar concentration of "hydrogen gas, in accordance with one embodiment of the present invention; and
Figures 2 illustrates a graphical representation of simulation for a series of temperature distribution for a gas mixture of H2- 31%, 02- 15% and N2 -54%, in accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Preferred embodiments will now be described in detail with reference to the accompanying drawings. The preferred embodiments do not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.
The present invention envisages a non-toxic gas propellant for the igniter of an airbag inflator system. The non-toxic gas propellant includes hydrogen gas, oxygen gas and an inert gas. The non-toxic gas propellant of the present

invention has high reaction rate and high heat generation per unit mass a gas mixture. The non-toxic gas propellant of the present invention may also be used in detonators used in mining application and other related applications.
The non-toxic gas propellant includes hydrogen gas in the range of 25 to 40% of the total volume of the gases mixture, oxygen in the range of 12 to 25% of the total volume of the gases mixture, and inert gas in the range of 35 to 62% of the total volume of the gases mixture. The mixture is compressed at a pressure of 10 to 25 bar.
In one embodiment of the present invention, the inert gas used is nitrogen. However, the present invention is not limited to any particular inert gas used. Accordingly, the inert gas utilized in the present invention may also be selected from the group consisting of neon, argon, xenon, helium and the like.
In one embodiment of the present invention, the non-toxic gas propellant includes hydrogen gas in the range of 30 to 35%. The hydrogen gas used in the present embodiment does not self ignite. Similarly, in another embodiment of the present invention, the non-toxic gas propellant includes oxygen gas in the range of 12- to 17%. Furthermore, in yet another embodiment of the present invention, the non-toxic gas propellant includes nitrogen gas in the range of 47% to 62%. Still further, in yet another embodiment of the present invention, the non-toxic gas propellant includes 3\% hydrogen gas, 54% nitrogen gas, and 15% oxygen gas. However, the present invention is not limited to any particular range of hydrogen gas, oxygen gas or nitrogen gas disclosed. Accordingly, the particular range of

hydrogen gas, oxygen gas or nitrogen gas is based on the reaction rate and heat generation required.
Combustion of hydrogen gas in air with oxygen gas is an exothermic reaction leading TO generation of heat.
2H2 + 02 -> 2H20 + Heat
Hydrogen gas has highest Calorific value/ unit mass in comparison with other fuels and also is non toxic in nature. The oxygen and nitrogen are combined in air.
Simulations of combustion reactions with different concentrations of hydrogen gas, oxygen gas and nitrogen gas are carried out to arrive at different rate of reactions. The combinations of different mass fractions analyzed are as follows:
• H2-29%,Air-71%
• H2 - 40% , 02 - 20% and N2 40%
• H2 - 40% , 02 - 25% and N2 35%
• H2 - 35% ,02-17% and N2 47%
• H2 - 35% , 02 - 17% and N2 47%
• H2 - 31 %, 02 - 15% and N2 54% •' H2 - 25% , 02 - 12% and N2 62 %
FIG. 1 illustrates a graphical representation of pressure rise Vs. time for different molar concentration of hydrogen gas. FIG. 2 illustrates a graphical

representation of simulation for a series of temperature distribution for a gas mixture of H2- 31%, 02- 15% and N2 - 54%.
TECHNICAL ADVANCEMENTS AND ECONOMIC SIGNIFICANCE
The propellant of the present invention is non-toxic in nature. Further, the non-toxic gas propellant of the present invention has high reaction rate. Furthermore, the non-toxic gas propellant does not self ignite. Moreover, the non-toxic gas propellant is adapted to generate a comparatively large amount of heat per unit mass of gas mixture. Also, the non-toxic gas propellant of the present invention is safe and does not create any health hazard. Additionally, the non-toxic gas propellant of the present invention is efficient for inflating an airbag inflator system. Further, the non-toxic gas propellant of the present invention is simple to manufacture.
The numeral values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope" of the invention and the claims unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein,
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whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We Claim:
1. A non-toxic gas propellant for an airbag inflator system
comprising:
• hydrogen gas in the range of 25 to 40% of the total volume of the gases mixture;
• oxygen gas in the range of 12 to 25% of the total volume of the gases mixture; and
• inert gas in the range of 35 to 62% of the total volume of the gases mixture;
wherein the mixture is compressed at a pressure of 10 to 25 bar.
2. The non-toxic gas propellant as claimed in claim 1, wherein said inert gas is nitrogen gas.
3. The non-toxic gas propellant as claimed in claim I, wherein said oxygen gas and nitrogen gas are combined in air.
4. The non-toxic gas propellant as claimed in claim 1, wherein said hydrogen gas is in the range of 30 to 35%.
5. The non-toxic gas propellant as claimed in claim 1, wherein said oxygen gas is in the range of 12 to 17%.
6. The non-toxic gas propellant as claimed in claim 1, wherein said nitrogen gas is in the range of 47 to 62%.
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7. The non-toxic gas propellant as claimed in claim 1, wherein hydrogen gas is 31%, nitrogen gas is 54% and oxygen gas is 15% of the total volume of said propellant.