FORM-2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
AIRBAG INFLATOR SYSTEM
TATA CONSULTANCY SERVICES LIMITED
an Indian Company of Nirmal Building, 9th Floor, Nariman Point, Mumbai - 400021,Maharashtra, India.

The following specification particularly describes the nature of the invention.

FIELD OF THE INVENTION
The present invention relates to safety devices for vehicles. Particularly, the present invention relates to an airbag inflator system for vehicles.
BACKGROUND OF THE INVENTION
Safety devices, such as airbags and seat belts are used in vehicles for protection of passengers. Airbags are used in vehicles 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.
Some of the prior art airbag inflator systems are as follows:
For example, US 5,577,769 patent having priority date as June 13, 1995 discloses a hybrid inflator for inflating vehicle air bags. The hybrid inflator includes a first pressure vessel containing a compressed gaseous fuel, and igniter assembly and a second pressure vessel containing a compressed inflator gas. In use, the compressed fuel gas is released into the compressed inflator gas vessel using an igniter assembly for ignition of the gaseous fuel.

Ignition of the gaseous fuel in the second pressure vessel causes a pressure and temperature rise which ruptures a burst disk in the second pressure vessel for gas release and inflation of an air bag. Further, the hybrid inflator of US5577769 patent uses Methane or H2 gas in the range of 35 bar (500psi) to 350 bar (5000psi), that may be harmful as the stored gas pressures are relatively high.
US 5,897,136 having priority date of 25 June, 1997 discloses an airbag inflator. The airbag inflator includes a housing having an interior and gas outlet ports communicating with the interior and open to outside the housing. First and second divider walls separate an inflation gas chamber and an initiator gas chamber from the interior. A pressurized inflation gas is stored in the inflation gas chamber. A pressurized combustible gaseous mixture is stored in the initiator gas chamber. An initiator is disposed within the initiator gas chamber and actuatable to ignite the pressurized combustible gaseous mixture. The second divider wall defining the initiator gas chamber is supported by the pressurized combustible gaseous mixture and resiliency deformable to force the first divider wall to rupture, permitting a flow of the pressurized inflation gas from the housing though the gas outlet port in response to actuation of the initiator. However, the airbag inflator of US 5,897,136 patent is unsafe as the combustible gas mixture is stored at high pressure and the inflator structure is different
US2003/0098572A1 having a priority date of August 29, 2000 discloses an inflator. The inflator includes C02 gas that charged into a housing of the inflator. The pressurized medium comprising an inert gas having a sound velocity of not less than 400 m/sec is charged into the inflator housing.

However, the inflator of the US20030098572 publication is unsafe to vehicle occupant.
US2003/0034642A1 with a priority date as August 17, 2001 describes a gas generation method via indirect ignition. Inflation apparatuses and methods disclose providing a supply of ignition material that indirectly ignited to assist in the inflation process. It includes a fluid storage chamber, a chamber opener and an indirect ignition charge. However, the gas generation method as disclosed in US2003/0034642 publication is in-efficient.
US7213838B2 having a priority date as October 21, 2003 discloses an inflator with inert gas in a tube like structure. More specifically, the inflator for an airbag includes an elongated pipe containing an inert gas and a pair of igniters. The igniters are positioned at opposite ends of the tube so that the inert gas can be generally evenly distributed out of a plurality of spaced apart openings positioned along the length of the tube. The openings are sealed until the inert gas reaches a predetermined pressure. The igniters are positioned at opposite ends and the openings are opened only after the inert gas reaches a predetermined pressure. However, the inflator of US7213838 patent is related to a protective cushion typically mounted on to the side of the vehicle cabin used for protecting a vehicle occupant during side impact.
US7380820B2 having apriority date as June 23, 2005 discloses a heated gas inflator for side airbag that uses a mixture of fuel gas, oxidizer gas and an inert gas as inflation fluid all enclosed in one chamber. More specifically,

the inflator for inflating an inflatable vehicle occupant protection device includes 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 heated gas inflator of US73 80820 is not compact.
US2008/0111358A1 with priority date as 14 November, 2006 discloses an inflator system with a chamber housing stored gas and an initiator. The inflator disclosed herein includes an initiator and a chamber that houses a quantity of stored gas. The initiator may be capable of actuating and causing the stored gas within the chamber to exit the chamber. A venting dome is also added to the initiator. The venting dome opens during deployment of the inflator. The venting dome also inverts and opens an aperture through which the stored gas may vent out of the inflator if the pressure of the stored gas exceeds a threshold level. However, the inflator system of US2008/0111358Al patent is not leak proof.
FR 2933929 with priority date as 17 July, 2008 describes an inflator with a gas generator, wherein rupturing of the 'Rupture disk (both 1& 2) is due to combustion of gas mixtures, unlike generation of gas by the igniter. The generator has a storage chamber for storing gas or reactive gas mixture at specific initial pressure. Another storage chamber stores another gas or reactive gas mixture that reacts with the former gas or gas mixture, at another initial pressure. An igniter is activated to cause simultaneous or

quasi-simultaneous rupture of storage caps when pressure at the interior of a cylindrical diffusion chamber is less than a threshold, liberation of the gases, their mixtures and their ignition and activation of a safety device i.e. airbag. The gas or reactive gas mixture in the storage chamber is selected from hydrogen, methane and a mixture of hydrogen or methane with helium, nitrogen, carbon dioxide or argon. The gas or reactive gas mixture in the storage chamber is selected from oxygen, air and a mixture of oxygen or air with helium, nitrogen, carbon dioxide or argon. However, the inflator FR 2933929 patent is structurally complex and may not be safe due to the presence of pressurized carbon dioxide.
Accordingly, there is a need for an airbag inflator system that is safe and non toxic. Further, there is a need for an airbag inflator system that is compact. Furthermore, there is a need for an airbag inflator system that is leak proof. Also, there is a need for an airbag inflator system that is simple in construction.
OBJECTS OF THE INVENTION
An object of the present invention is to provide an airbag inflator system that is compact and adapted to be positioned into a steering wheel of a vehicle.
Another object of the present invention is to provide an airbag inflator system that is leak proof.
Yet another object of the present invention is to provide an airbag inflator system that is adapted to store propellant gases at low pressures for ensuring safety of the passengers in all driving conditions.

Still another object of the present invention is to provide an airbag inflator system that is simple in construction.
One more object of the present invention is to provide an airbag inflator system that is comparatively inexpensive.
Also, an object of the present invention is to provide an airbag inflator system that is robust in construction.
One more objective of this present invention is to provide an airbag inflator system that uses non toxic gas mixture, which is safe in stored condition, as well as during airbag inflation
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided an airbag inflator system. The airbag inflator system includes a double chambered housing, a frangible wall, a gas propellant, a triggering circuit, at least one micro gas filling and leak prevention port and an airbag mounting plate. The double chambered housing is separated by a dome shaped frangible partition to divide the housing into an igniter chamber and a reaction chamber. The partition is adapted to collapse at 90 bar. The reaction chamber contains inflation gas at a pressure of 40 to 60 bar consisting predominantly of inert gas. The frangible wall is defined on the reaction chamber for propelling inflation gas into the conduit leading to an air bag. The frangible wall is adapted to collapse at a pressure greater than the pressure at which the partition collapses. The gas propellant is filled in the igniter chamber. The gas propellant is contained inside the igniter chamber

at a pressure of 10 to 25 bar. The triggering circuit is fitted to the igniter chamber. The at least one micro gas filling and leak prevention port is adapted to facilitate filling and storing of gases for long duration of time. The airbag mounting plate is adapted to mount a folded airbag on top of said double chambered housing.
Preferably, the inert gas is nitrogen.
Typically, the propellant gas includes oxygen in the range of 12 to 25% of the total volume of the propellant gas.
Typically, the propellant gas also includes hydrogen in the range of 25 to 40% of the total volume of the propellant gas.
Preferably, the propellant gas includes hydrogen gas, oxygen gas and nitrogen gas.
Furthermore, the frangible wall has deformable slits.
Typically, the deformable slits are adapted to be forced open when subjected to a predetermined internal pressure.
Preferably, the frangible wall has capsule shape.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The invention will now be described in relation to the accompanying drawings in which,
Figure 1 illustrates an exploded view of an airbag inflator system, in accordance with one embodiment of the present invention;
Figures 2 illustrates an assembled view of the airbag inflator system of Figure 1;
Figure 3 illustrates assembled perspective view of the airbag inflator system of figure 1 disposed within a steering wheel of a vehicle;
Figure 4 illustrates an exploded view of the Figure 3;
Figure 5a to 5c illustrates perspective views of the airbag inflator system of figure 1 disposed within a steering wheel;
Figure 6a to 6f illustrates simulation of the airbag inflator system of figure 1;
Figures 7a to 7e illustrates various views of the frangible wall before and after rupturing of the same;
Figure 7f to 7h illustrates perspective views of frangible wall opening pattern;

Figure 8a to 8d illustrates tank pressure set up;
Figure 9 illustrates a tank pressure curve;
Figure 10 illustrates a graph for the rate of combustion (Pressure Vs time) for different gas contractions in the ignition chamber; and
Figure 11 illustrates igniter voltage rise time and the final step up voltage before arcing.
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.
Referring to Figure 1 and Figure 2, an airbag inflator system 100 includes a double chambered housing 102, a frangible wall 104, a gas propellant, a triggering circuit 106, at least one micro gas filling and leak prevention port and an airbag mounting plate 114.
The double chambered housing 102 is separated by a dome shaped frangible partition 108 to divide the housing 102 into an igniter chamber and a reaction chamber. The partition 108 is adapted to collapse at 90 bar. In one embodiment of the present invention, the partition 108 is hemispherical in

shape. The reaction chamber contains inflation gas at a pressure of 40 to 60 bar consisting predominantly of inert gas. In one embodiment of the present invention, the inert gas is nitrogen gas. In one embodiment of the present invention, the reaction chamber may also include oxygen gas in the range of 0 to 15%. In yet another embodiment of the present invention, the reaction chamber may also include hydrogen gas in the range of 5 to 10%. The reaction chamber may include a gas filling port for filling propellant gas under pressure. The port may be adapted to function both as filling and gas sealing port for facilitating leak proof filling and storing of the propellant gas.
The frangible wall 104 is defined on the reaction chamber for propelling inflation gas into the conduit leading to an air bag. The frangible wall 104 is adapted to collapse at a pressure greater than the pressure at which the partition 108 collapses. In one embodiment of the present invention, the frangible wall 104 is adapted to rupture at 100 bar. However, the present invention is not limited to a particular pressure for rupturing the frangible wall 104. In one embodiment of the present invention, the frangible wall 104 has capsule shape. However, the present invention is not limited to any particular shape of the frangible wall 104. The frangible wall 104 includes deformable slits 110 (shown in Figure 7c and 7e). The deformable slits 110 are adapted to be forced open when subjected to a predetermined internal pressure. The deformable slits 110 provided on the frangible wall 104 ensures that the frangible wall 104 blooms like lotus petals in optimum amount of time thus releasing the gas into the airbag safely. The deformable slits 110 are adapted to have various configurations such as 'STAR' notched configuration, "V" shape, and the like to achieve optimum rupture pattern.

In one embodiment of the present invention, depth of the deformable slits 110 varies between 0.05 mm to 0.25mm. The deformable slits 110 are designed to achieve optimum rupturing of the frangible wall 104 for different pressures ranges, such as 100 bar to 300 bar. By varying the size, shape and position of the notches, the rupture pattern and the orifice size can be varied to achieve desired mass flow rate or gas exit velocity. Further, the frangible wall 104 size may vary between 20 mm to 70 mm and thickness between 0.2 mm to 1 mm for different pressure ranges. Furthermore, the frangible wall 104 may be of aluminum, Mild Steel, Stainless Steel or any other suitable material. However, the present invention is not limited to any particular material used for manufacturing the frangible wall 104.
The gas propellant is filled in the igniter chamber. The gas propellant is contained inside the igniter chamber at a pressure of 10 to 25 bar. Preferably, the propellant gas includes hydrogen, oxygen and nitrogen. In one embodiment of the present invention, the propellant gas includes oxygen in the range of 12 to 25% of the total volume of the propellant gas. Further, in one embodiment of the present invention, the propellant gas also includes hydrogen in the range of 25 to 40% of the total volume of the propellant gas. In one embodiment of the present invention, the igniter chamber may include a port for filling propellant gas under pressure. The port may be adapted to function both as filling and gas sealing port for facilitating leak proof filling and storing of the propellant gas. Although, in the present embodiments of the present invention, the propellant gas is described as a combination of particular gases having particular range, however, the present invention is not limited to the embodiments described. Further, in other

embodiments of the present invention, the igniter gases may be LPG, CNG, Methane or the like.
The triggering circuit 106 is fitted to the igniter chamber. More specifically, the triggering circuit 106 is fitted at an outer end of the igniter chamber. The triggering circuit 106 is adapted for igniting the propellant gas. In one embodiment of the present invention, the triggering circuit 106 includes at least one pair of electrodes adapted to generate an arc there-between, insulators adapted to isolate the electrodes and an electric circuit adapted to generate a high voltage arc between the electrodes.
Further, the airbag inflator system 100 includes an airbag housing cover 112, an airbag mounting plate 114, and a covering plate 116. The airbag is fixed to the airbag mounting plate 114 by four screws and the airbag mounting plate 114 along with the airbag is in turn mounted onto the airbag housing cover 112. The whole inflator unit may be further mounted to a top steering cover 118 that may be snug fitted to the bottom steering cover of the steering wheel assembly.
In one embodiment of the present invention, the airbag inflator system 100 may include a muffler disposed above the partition 108 to prevent the debris of the partition 108 from flying into the airbag. The muffler is also adapted to reduce the noise level of the combustion by around 5-10 db. In one embodiment of the present invention, the airbag inflator system 100 has a volume of 120 x 120 x 80mm that could be easily incorporated into a steering wheel 120 of a vehicle (shown in Figures 3, 4 and 5a to 5c). Further, the airbag inflator system 100 of the present invention is symmetrical in

construction. This symmetrical design of the airbag inflator system 100 apart from providing simple structure, also ensures that the overall cost of the airbag inflator system 100 be maintained low. In one embodiment of the present invention, the airbag inflator system 100 is of annealed stainless steel and hermetically sealed and designed to ensure safety. Also, the airbag inflator system 100 is adapted to withstand instantaneous shock and high stress levels at the time of combustion.
In the event of a crash, the hydrogen gas is ignited by the triggering circuit 106. The combustible hydrogen gas in the presence of oxygen releases large amount of heat and raises the temperature about 2000 deg c and pressure to 150 bars. At this moment the partition 108 ruptures and the propellant gas is released into the reaction chamber. This raises the temperature of the Nitrogen gas which in turn raises the pressure to grater than 150 bar. Further, releasing of the propellant gas into the reaction chamber also expands the nitrogen gas. At this moment, the frangible wall 104 ruptures and releases the propellant gas to the inflatable device (or a test tank) and inflates it. In one embodiment of the present invention, the whole process from combustion to inflation completes in a matter of less than 30 milliseconds.
TEST ANALYSIS:
1. Simulation of the Airbag inflator:
The FE Analysis of the air bag inflator 100 and the frangible wall 104 was done using LS-Dyna software. The inflator 100 was evaluated for Yield strength and the frangible wall 104 was evaluated for failure

strength and buckling under various pressures. Different configurations of the inflator 100 and the frangible wall 104 were simulated and the results of the same are shown in Figures 6a to 6f. 2. Tank Pressure Test:
Referring to Figures 8a to 8d, the air bag inflator system 100 of the present invention is subjected to a tank pressure test to study the airbag inflation pressure and time immediately after the gas oozes out into the airbag. The tank pressure test gives the pressure -time curve which is crucial for the above study. The Tank pressure test consists of a metal tank with pressure sensors mounted at various locations. The air bag inflator 100 is mounted on top of the metal tank and all the gases in required molar ratios are filled into the inflator. The inflator is fired using a remote device. Upon firing, combustion of gases takes place and both the dual chamber rupture disk ruptures out releasing gas into the metal tank. The pressure - time data is captured through lab view and plotted. Further, the tank pressure curve is illustrated in Figure 9.
Figure 10 illustrates a graph for the rate of combustion (Pressure Vs time) for different gas contractions in the ignition chamber. Figure 11 illustrates the igniter voltage rise time and the final step up voltage before arcing.
TECHNICAL ADVANCEMENTS AND ECONOMIC SIGNIFICANCE
The airbag inflator system of the present invention is compact and adapted to be positioned into a steering wheel of a vehicle. Further, the airbag inflator system is leak proof. Furthermore, the airbag inflator system is adapted to store propellant gases at low pressures for ensuring safety of the passengers

in all driving conditions. Moreover, the airbag inflator system that is simple in construction. Also, the airbag inflator system is comparatively inexpensive. Additionally, the airbag inflator system is robust in construction. Also the inflator uses non toxic gas mixture.
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, 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. An airbag inflator system comprising:
• a double chambered housing separated by a dome shaped frangible partition to divide the housing into an igniter chamber and a reaction chamber, wherein said partition is adapted to collapse at 90 bar, and wherein said reaction chamber contains inflation gas at a pressure of 40 to 60 bar consisting predominantly of inert gas;
• a frangible wall defined on the reaction chamber for propelling inflation gas into the conduit leading to an air bag, wherein said frangible wall is adapted to collapse at a pressure greater than the pressure at which the partition collapse;
• a gas propellant filled in said igniter chamber, wherein the gas propellant is contained inside said igniter chamber at a pressure of 10 to 25 bar;
• a triggering circuit fitted to said igniter chamber;
• at least one micro gas filling and leak prevention port to fill and store gases for long duration of time; and
• an airbag mounting plate to mount a folded airbag on top of said double chambered housing.
2. The airbag inflator system as claimed in claim 1, wherein said inert gas is nitrogen gas.

3. The airbag inflator system as claimed in claim 1, wherein said propellant gas includes oxygen in the range of 12 to 25% of the total volume of said propellant gas.
4. The airbag inflator system as claimed in claim 1, wherein said propellant gas also includes hydrogen in the range of 25 to 40% of the total volume of said propellant gas.
5. The airbag inflator system as claimed in claim 1, wherein said propellant gas includes hydrogen, oxygen and nitrogen.
6. The airbag inflator system as claimed in claim 1, wherein said frangible wall has deformable slits.
7. The airbag inflator system as claimed in claim 1, wherein said partition is hemispherical.
8. The airbag inflator system as claimed in claim 6, wherein said deformable slits are adapted to be forced open when subjected to a predetermined internal pressure.
9. The airbag inflator system as claimed in claim 1, wherein said frangible wall has capsule shape.
10. The airbag inflator system as claimed in claim 1, wherein said micro gas filling port is adapted to function both as filling and gas

sealing port for facilitating leak proof filling and storing of the propellant gas.