2. Description of Related Art The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. In the event of an accident, an accelerometer within the vehicle measures the abnormal deceleration and triggers the expulsion of rapidly expanding gases from an inflator. The expanding gases fill the airbags, which immediately inflate in front of the driver and passenger to protect them from impact against the windshield. Side impact airbags, known as inflatable curtains, have also been developed in response to the need for protection from impacts in a lateral direction, or against the side of the vehicle. An inflatable curtain may have one or more separately inflated cushions.

Side impact cushions are often designed to unfold or unroll downward to inflate beside a person to keep the person from hitting the door or window during lateral impact.

Since a vehicle occupant may be leaning forward, reclined in the seat, or at any position between, such cushions are often made somewhat long to ensure that the occupant hits the cushion. If multiple cushions are fed by a single inflator positioned either fore or aft of the cushions, an especially long gas flow path exists between the inflator and the cushion furthest from the inflator. Thus, the outermost extents of the inflatable curtain may receive insufficient inflation gas pressure to inflate to the optimal protective pressure.

Even with somewhat shorter cushions, rapid and even inflation can be difficult to achieve with known inflator designs. Many existing inflators eject inflation gases outward radially; consequently, the inflation gases are not propelled along the length of the cushion, but are directed into the cushion near the inflator. The outer regions of the cushion are still inflated later than those closest to the inflator.

Additionally, some inflatable curtain systems are somewhat expensive due to the need for multiple inflators, attachment mechanisms, and the like. Many inflatable curtain

systems require the use of a gas conduit that conveys gas from the inflator to the inflatable curtain. Some known inflators require the use of multiple initiators that add to the manufacturing expense and timing requirements of the inflator.

Furthermore, many inflators produce thrust upon activation. As a result, somewhat complex attachment mechanisms must often be used to affix the inflators to the vehicle to ensure that the inflators do not dislodge themselves during deployment. Such additional parts increase the cost of the inflatable curtain system, as well as the time and expense required to install the inflatable curtain system in a vehicle.

Accordingly, a need exists for an inflator and related methods that remedy the problems found in the prior art. Such an inflator should preferably provide relatively even and rapid inflation of the associated inflatable curtain, preferably without requiring multiple inflators for a single curtain. Such an inflator should also preferably be simple and inexpensive to manufacture and install.

SUMMARY OF THE INVENTION The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available inflators. The invention as embodied and broadly described herein is a dual flow inflator. According to one configuration, the inflator may comprise a gas chamber with a first end disposed within a first inlet port of the inflatable curtain and a second end disposed within a second inlet port of the inflatable curtain. The gas chamber may comprise one unitary body. The first and second inlet ports may be tightly affixed to the gas chamber such that gas is unable to escape from the inflatable curtain between the inlet ports and the gas chamber.

The gas chamber may have a first exit orifice positioned at the first end and a second exit orifice positioned at the second end. Each exit orifice may have a sealed configuration that does not permit gas flow, and an open configuration, in which inflation gases flow relatively freely out of the gas chamber through the exit orifice. Each exit orifice may take the form of a diffuser that forms an interior wall with an opening covered by a burst disc; the burst discs may be removed from the openings via a pressure shock induced by combustion within the gas chamber. Burst disc retention members may be disposed outside the openings to capture the burst discs and ensure that they do not damage the inflatable curtains.

Each exit orifice may also have a gas guide diffuser disposed outside the opening to control the flow of inflation gas out of the exit orifice. The gas guide diffusers may be aligned with the longitudinal axis of the inflator so that inflation gases are ejected along the longitudinal axis. The gas guide diffusers of the first and second orifices may be directed opposite to each other so that thrust from the first exit orifice substantially negates the thrust from the second exit orifice, and vice versa.

The inflator may have an initiator disposed near or partially within the gas chamber to activate a gas-producing material to create first and second gas flows through the first and second exit orifices, respectively. The gas-producing material may be a liquid/gas mixture that has been cryogenically inserted into the gas chamber in solid form. Whether cryogenic or standard gas-producing material is used, the gas-producing material may be inserted into the inflator through a salable fill port or into the interior of the inflator prior to assembly of the inflator components. The initiator may heat the liquid/gas mixture to cause the pressure shock that removes the burst discs from the openings, thereby moving the first and second exit orifices into the open configuration.

According to one alternative embodiment, an inflator may comprise a gas chamber constructed of multiple parts. The gas chamber may have two vessels and a bulkhead.

Each of the vessels may have a generally tubular shape with an interior end and an exterior end. The bulkhead may also have a tubular shape with two apertures designed to be aligned with the interior ends of the vessels. The vessels may be affixed to the bulkhead through a method such as welding. First and second exit orifices may be disposed on the exterior ends of the first and second vessels, respectively.

In place of the openings and burst discs of the first embodiment, the first and second exit orifices of the second embodiment may take the form of scored, or notched, surfaces that open when the pressure within the gas chamber exceeds the tear strength of the scored regions. The scored surface may open to form a suitable exit nozzle.

As with the previous embodiment, a gas-producing material such as a compressed gas and liquid mixture may be thermally activated by an initiator to provide first and second gas flows through the first and second exit orifices, respectively. In order to ensure that both scored surfaces burst completely and simultaneously, two pistons may be positioned within the gas chamber on either side of the initiator. When the gas-producing material between the pistons expands, the increasing pressure drives the pistons outward, toward the exit orifices. The result is an increase in the pressure between the pistons and

the exit orifices; this pressure increase induces failure of the scored regions to open the first and second exit orifices.

According to another alternative, the inflator may comprise a gas chamber with two vessels affixed to a generally spherical bulkhead. Each vessel may have an exit orifice that takes the form of a compression closure, such as a crimped opening. The crimped opening may have two lips pressed flat together and attached through a method such as welding. As with the scored region, the crimped opening opens in response to a pressure increase within the gas chamber. In the alternative, some physical puncture mechanism may be used to open the crimped opening when activated by the initiator.

More specifically, the inflator may have pistons like those described in connection with the previous embodiment. Each of the pistons may have a puncture member designed to impact the associated exit orifice, thereby opening the lips to permit escape of the pressurized inflation gases.

In yet another embodiment, the entire gas chamber may have a generally spherical shape. The gas chamber may be made from two hemispherical portions attached together.

Each hemispherical portion may have an exit orifice; the exit orifices may be positioned opposite each other to permit the inflation gases to flow out from the gas chamber in opposite directions. The exit orifices may take the form of openings with burst discs, as in the first embodiment.

Through the use of the inflators of the present invention, cost savings may be obtained through the elimination of gas conduits, complex attachment features, and redundant inflators and initiators. Additionally, more rapid and even inflation of the inflatable curtains may be obtained. As a result, the availability and effectiveness of vehicular airbag systems may be enhanced.

The invention also comprises a dual flow inflator comprising a gas chamber coupled to a first ejection orifice and a second ejection orifice. The first orifice has a first effective cross-sectional area and is fluidly coupled to the gas chamber. The second orifice, similarly, has a second effective cross-sectional area and is fluidly coupled to the gas chamber, where the cross-sectional areas of the orifices are different.

When the inflator releases the inflator gases, the difference between the two effective cross-sectional areas creates two different mass flow rates exiting the inflator.

The mass flow rate of a gas is a function of the size of the orifice from which the gas is ejected. By controlling the size of the orifice, an inflator with two orifices can eject gas at

two different mass flow rates. Other mechanisms of controlling the mass flow rates may also be employed, such as placing obstructions in the orifice to limit the cross-sectional area or by diverting a flow of gas away from the inflatable curtain.

The gas chamber may also have a first retention orifice and a second retention orifice. The first and second retention orifices are configured to have an open state and a closed state. The closed state may be accomplished by placing burst disks or other sealing mechanisms in front of each of the retention orifices. The open state occurs when the burst disks are forced through the retention orifices to allow gas to exit the inflator. The retention orifices may also function similarly to the ejection orifices by controlling the mass flow rate of gas exiting the inflator. The effective cross-sectional area of each of the retention orifices can be adjusted such that the two retention orifices eject gas at different mass flow rates.

The first and second ejection orifices or the first and second retention orifices may be configured to provide flows of gas in substantially opposite directions. Such a configuration could be accomplished with a generally elongated inflator having openings at opposing ends of the inflator. When the inflator is placed in operation, the first ejection orifice or retention orifice ejects gas in a first direction, while the second ejection orifice or retention orifice ejects gas in a substantially opposite, second direction.

The two gas flows being ejected from the inflator in opposite directions also minimize the thrust that is produced by the inflator. However, because the different mass flow rates generate different magnitudes of thrust, the inflator may not be entirely thrust neutral. A thrust neutral configuration can be created along a single axis even with two gas flows of different mass flow rates simultaneously exiting the inflator. This may be accomplished by angling one of the ejection orifices ejecting a gas. By angling an ejection orifice, the thrust will be divided into longitudinal and transverse components. The angle of the ejection orifice can be defined so that the longitudinal component of the angled ejection orifice is substantially equal and opposite to a non-angled ejection orifice. Thus, the inflator may be thrust neutral in a single direction.

The use of two different gas flows having different mass flow rates from a single inflator allows for a large degree of control in deploying inflatable curtains. The different gas flows can be established to inflate two different sized volumes, such as two different sized sections in an inflatable curtain. The gas flow with the larger mass flow rate could inflate a larger volume and a smaller gas flow with a smaller mass flow rate could inflate a

smaller volume. Alternatively, the two different gas flows can be employed to inflate two substantially different volumes at different times or at different pressures.

The invention may also be accomplished by coupling together two inflators each having gas flows of different mass flow rates. By coupling the inflators together, the module will function similarly to an inflator having two ejection orifices with two different gas flows. The inflator module may be substantially thrust neutral by orienting the ejection orifices in substantially opposite directions.

The present invention also comprises a dual stage biaxial inflator having a primary gas chamber, a flow restrictor, and a secondary gas chamber is disclosed. The inflator may comprise a primary gas chamber with a first end disposed within a first inlet port of the inflatable curtain and a second end disposed within a second inlet port of the inflatable curtain. The primary gas chamber may comprise one unitary body. The first and second inlet ports may be tightly affixed to the gas chamber such that gas is unable to escape from the inflatable curtain between the inlet ports and the gas chamber. The secondary gas chamber may be in gaseous communication with the primary gas chamber through the flow restrictor, which is positioned between the primary gas chamber and the secondary gas chamber. The inflator may additionally include an initiator in communication with at least one of the gas chambers for initiating a flow of gas through the exit orifices.

The primary gas chamber may have a first exit orifice positioned at a first end and a second exit orifice positioned at a second end. Each exit orifice may have a sealed configuration that does not permit gas flow, and an open configuration, in which inflation gases flow relatively freely out of the gas chamber through the exit orifice. Each exit orifice may take the form of an interior cap with an opening covered by a burst disc; the burst discs may be removed from the openings via a pressure shock induced by combustion within the gas chamber. Burst disc retention members may be disposed outside the openings to capture the burst discs and ensure that they do not damage the inflatable curtains.

Each exit orifice may also have an ejection nozzle that controls the flow of inflation gas out of the exit orifice. The ejection nozzles may be aligned with the longitudinal axis of the inflator so that inflation gases are ejected along the longitudinal axis. The ejection nozzles of the first and second exit orifices may be directed opposite to each other so that thrust from the first exit orifice substantially negates the thrust from the

second exit orifice, and vice versa. As a result, the inflation gases are ejected in directions substantially opposite each other.

The secondary gas chamber is positioned in gaseous communication with the primary gas chamber through the flow restrictor. The flow restrictor has a flow restrictor orifice that in some inflators has a sealed configuration and an open configuration. In those inflators where the flow restrictor has only an open configuration, inflation charges placed within the primary and secondary gas chambers may be allowed to mingle. In those inflators that include a flow restrictor having a sealed configuration, the seal may be formed by a frangible seal such as a burst disc, scored surface, or compression seal.

Inflators that have burst discs may also have burst disc retention members to retain the burst disc after initiation of the inflator.

The flow restrictor that connects the primary and secondary gas chambers may simply include a restricted flow channel. This channel is defined using methods known in the art to be sufficiently narrow to meter the flow of an inflation gas produced by the inflation charge of the secondary gas chamber such that the flow of gas is lengthened out to a predetermined duration. This duration could be selected by tuning the diameter of a restricted flow channel.

The inflator may have an initiator disposed within the assembly that activates a gas-producing material to create first and second primary gas flows through the first and second exit orifices of the primary gas chamber, respectively. The initiator assembly may be positioned within the primary gas chamber, the secondary gas chamber, or both gas chambers.

The inflator of the invention may also include a gas generant, or gas-producing material in the form of a solid, liquid, gas, or liquid/gas mixture that has been cryogenically inserted into the gas chambers in solid form. The initiator of the inflator is positioned to heat the liquid/gas mixture, thus causing gas generation and initiating the rise in pressure or pressure shock. This increase in pressure or pressure shock may remove the burst discs from the openings or otherwise place the exit orifices into their open configurations. This change in configuration allows the flows of gas from the exit orifices to begin.

The inflator of the invention is capable of providing primary and secondary gas flows to inflate and then maintain the inflation of an airbag or inflatable curtain. The primary gas flow is provided primarily by the inflation charge housed within the primary

gas chamber or chambers. This primary gas flow is split into a first and a second primary gas flow, proceeding from the first and second exit orifices, respectively, of the primary chamber. This primary gas flow is largely responsible for the initial inflation of the airbag or inflatable curtain. The secondary gas flow is produced primarily from the inflation charge housed within the secondary gas chamber or chambers. This secondary flow of gas is triggered either passively as the pressure of the primary gas chamber decreases, or actively by a pressure gradient which could be created by an initiator associated with the secondary gas chamber. This secondary flow of gas proceeds out of the secondary gas chamber into the primary gas chamber, and is then split into first and second secondary gas flows which are ejected from the first and second exit orifices, respectively. This secondary flow of gas may be used to maintain the inflation of the airbag or inflatable curtain, or, in some cases, to reinflate it. In addition, in so-called"smart"airbag systems, the secondary flow of gas may be initiated in response to collisions of a particular nature or severity, or initiated only when the vehicle occupant to be protected by the inflatable cushion is of a certain size or weight.

According to one alternative, the inflator may comprise multiple secondary and/or primary gas chambers in order to provide a controllable, customizable flow of gas. The gas chambers may be vessels having a generally tubular shape. As discussed briefly above, these chambers may have frangible seals such as the openings and burst discs discussed above, or scored, or notched, surfaces that open when the pressure within the gas chamber exceeds the strength of the scored regions. The scored surface may open to form a suitable exit nozzle. Additionally, the frangible seal may be a compression closure, such as a crimped opening. The crimped opening may have two lips pressed flat together and attached through a method such as welding. As with the scored region, the crimped opening opens in response to a pressure shock and/or increase within the gas chamber, and may be configured to form a suitable exit nozzle upon opening. In each of these alternatives, some physical puncture mechanism may be used to assure that the frangible seal opens when activated by the initiator.

As with the previous inflator, a gas-producing material such as a compressed gas and liquid mixture may be thermally activated by an initiator to provide first and second primary and secondary gas flows through the first and second exit orifices, respectively.

In order to ensure that the frangible seals over both exit orifices burst completely and

simultaneously, tight tolerancing of the burst discs, scored surfaces, or compression seals may be implemented.

According to another embodiment of the invention, the dual stage biaxial inflator for a vehicular airbag system may include a first primary gas chamber having a first longitudinal axis and a first exit orifice configured to provide a first primary gas flow oriented substantially along the longitudinal axis, the first exit orifice having an open and a closed configuration. Additionally, the inflator may include a second primary gas chamber having a second longitudinal axis and a second exit orifice configured to provide a second primary gas flow oriented substantially along the longitudinal axis; the second exit orifice having an open and a closed configuration. The inflator additionally has a secondary gas chamber in gaseous communication with said first and second primary gas chambers configured to provide a secondary gas flow and a flow restrictor positioned between each primary gas chamber and the secondary gas chamber. The inflator also includes an initiator in communication with the interior of one of said gas chambers, the initiator being configured to selectively initiate a flow of gas through the exit orifice.

In this inflator, the secondary gas chamber may be located between the first and second primary gas chambers. The first and second exit orifices of the first and second primary gas chambers may be configured to provide first and second primary gas flows which have substantially equivalent amounts of gas. Further, the first and second exit orifices may be configured to provide first and second primary gas flows which have different amounts of gas. In addition, the inflator may be constructed so that the first longitudinal axis and the second longitudinal axis are equivalent. In inflators where the first and second primary gas flows are identical, and where the first and second longitudinal axes are identical, a substantially zero-thrust inflator may be provided. Such a zero-thrust inflator may be provided under the first embodiment, as well. In this inflator, each primary gas chamber may have its own initiator. Additionally, the secondary gas chamber may have its own initiator.

Through the use of the inflators of the present invention, cost savings may be obtained through the elimination of gas guides, complex attachment features, and redundant inflators and initiators. Additionally, more rapid and even inflation of the inflatable curtains may be obtained, and sustained inflation of the inflatable curtains may be achieved. As a result, the availability and effectiveness of vehicular airbag systems may be enhanced.

These and other features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the manner in which the above-recited and other advantages and objects of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: Figure 1 is a perspective view of a vehicle with an inflatable curtain that incorporates one embodiment of an inflator according to the invention; Figure 2 is a side elevation, section view of the inflator of Figure 1; Figure 3 is a side elevation, section view of an alternative embodiment of an inflator according to the invention; Figure 4 is a side elevation, section view of another alternative embodiment of an inflator according to the invention; and Figure 5 is a side elevation, section view of yet another alternative embodiment of an inflator according to the invention.

Figure 6 is a perspective view of a vehicle with an inflatable curtain that incorporates one embodiment of an inflator according to the invention.

Figure 7 is a cross-sectional view of an inflator having two different sized ejection orifices.

Figure 8 is a cross-sectional view of an inflator having two different sized retention orifices.

Figure 9A is an end view of an obstructed orifice embodiment having a first effective cross-sectional area.

Figure 9B is an end view of an obstructed orifice embodiment having a second effective cross-sectional area.

Figure 10A is an end view of another obstructed orifice embodiment implementing a pin obstruction and having a first effective cross-sectional area.

Figure 10B is an end view of another obstructed orifice embodiment implementing a pin obstruction and having a second effective cross-sectional area.

Figure 11 is a cross-sectional view of an inflator having a bleed line.

Figure 12 is a cross-sectional view of a dual-inflator inflator module.

Figure 13 is a cross-sectional view of an inflator having an angled end.

Figure 14 is a cross-sectional view of an inflator having two different sized choked orifices.

Figure 15 is a side view of an inflator and an inflatable curtain.

Figure 16 is a perspective view of a vehicle with an inflatable curtain that incorporates one embodiment of an inflator according to the invention; Figure 17 is a side elevation cross sectional view of the inflator of Figure 1; and Figure 18 is a side elevation cross sectional view of an alternative embodiment of an inflator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as represented in Figures 1 through 18, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.

The present invention provides an apparatus and method whereby problems associated with previously known inflators can be resolved. More specifically, through the use of counterbalancing axial flows, a thrust neutral design may be obtained, thereby eliminating the complexity of axially supported inflator mounting. Furthermore, a single- initiator configuration provides simplicity of manufacturing and activation.

Yet further, inflation gas can be simultaneously injected into multiple inlet ports in an inflatable curtain to enhance the speed of curtain deployment. Through the use of axial

flow, inflation gas can be injected away from exit orifices of the inflator. Hence, the inflatable curtain deploys more evenly to provide better occupant protection. The manner in which these principles are utilized in the present invention will be shown and described in greater detail in the following discussion.

Referring to Figure 1, an inflatable curtain 10 according to one possible embodiment the invention is shown installed in a vehicle 12. The inflatable curtain 10 may form part of an airbag system configured to protect one or more vehicle occupants against lateral impact through the formation of a protective curtain beside the occupants.

The vehicle 12 has a longitudinal direction 13, a lateral direction 14, and a transverse direction 15. The vehicle 12 further has front seats 16 laterally displaced from first lateral surfaces 17, or front doors 17, as shown in the vehicle 12 of Figure 1. The vehicle 12 also has rear seats 18 laterally displaced from second lateral surfaces 19, or rear doors 19, as depicted. As shown, two such inflatable curtains 10 may be used: one for the driver's side of the vehicle 12, and the other for the passenger's side.

One or more accelerometers 20 or other similar impact sensing devices detect sudden lateral acceleration (or deceleration) of the vehicle 12 and transmit electric signals via electric lines 22 to one or more inflators 24 that provide pressurized gas to inflate the inflatable curtains 10. As shown in Figure l, a single inflator 24 may be used to inflate each of the inflatable curtains 10. The inflators 24 may be affixed to the vehicle 24 through the use of relatively simple mounting brackets 26.

The inflators 24 may be positioned approximately midway along the longitudinal length of the inflatable curtains 10 to provide relatively rapid and even inflation, in a manner that will be described in greater detail subsequently. Of course, the position and attachment of the inflators 24 may be varied in a number of ways from the configuration depicted in Figure 1.

Each of the inflators 24 may take the form of a hollow pressure vessel containing a chemically reactive material and/or compressed gas that can be activated or released upon application of electricity to provide an outflow of inflation gases. In the exemplary configuration of Figure 1, the inflators 24 are partially enveloped within the inflatable curtains 10 so that inflation gases exiting the inflators 24 flow directly into the inflatable curtains 10. The inflators 24 may operate with such rapidity that, before the vehicle 12 has fully reacted to the impact, the inflatable curtains 10 have inflated to protect vehicle occupants from impact.

Optionally, the accelerometers 20 may be stowed within an engine compartment 30 or dashboard 32 of the vehicle 12. A controller (not shown) may also be used to process the output from the accelerometer 20 and control various other aspects of a vehicle safety system of the vehicle 12. If the accelerometers 20 are remotely positioned, the electric line 22 and/or other control wiring may be disposed along the A pillars 34 of the vehicle 12, on either side of the windshield 35, to reach the inflators 24. Alternatively, each accelerometer 20 may be positioned near one of the inflators 24, as shown in Figure 1.

The inflators 24 and the inflatable curtains 10 may be attached to roof rails 36 of the vehicle 12. Depending on the model of the vehicle 12 and the desired configuration of the inflatable curtains 10, airbag components may also be disposed along the B pillars 37, C pillars 38, and/or D pillars 39.

The inflatable curtains 10 shown in Figure 1 are configured to protect not only occupants of the front seats 16, but those of the rear seats 18 as well. Thus, each inflatable curtain 10 may have a first protection zone 40 configured to inflate between the front seats 16 and one of the front doors 17, and a second protection zone 42 configured to inflate between the rear seats 18 and one of the rear doors 19. The first and second protection zones 40,42 may be essentially separate, and may be in fluid communication with each other only through the inflators 24. In the alternative, the first and second protection zones 40,42 may have an alternative flow path through which fluid can pass between the first and second protection zones 40,42, even when gas is not able to flow through the inflator 24 between the first and second protection zones 40,42.

The first and second protection zones 40,42 of each inflatable curtain 10 may be attached together through the use of a connection zone 44 positioned between the protection zones 40,42. The connection zone 44 may provide a flow path through which gases can flow between the first and second protection zones 40,42, or may simply convey tension between the first and second protection zones 40,42 to keep the first and second protection zones 40,42 in place.

Each of the inflatable curtains 10 may have a front tether 46 attached to the A pillar 34 and a rear tether 48 attached to the roof rail 36 to exert tension on the inflatable curtains 10 to keep them in place during inflation and impact. Those of skill in the art will recognize that the tethers 46,48 may also be attached to other parts of the vehicle 12, such

as the B pillars 37, C pillars 38, and/or D pillars 39. The tethers 46,48 may be constructed of standard seatbelt webbing or the like.

Although each inflatable curtain 10 in Figure 1 has two protection zones 40,42, the invention encompasses the use of inflatable curtains with any number of protection zones. Thus, if desired, each of the inflatable curtains 10 may be extended to have one or more protection zones positioned to protect occupants of extra seats 50 behind the rear seats 18 from impact against third lateral surfaces 52 of the vehicle 12. Additional inflators 24 may be used to inflate such additional protection zones.

The inflators 24 may be uniquely configured to provide rapid, even inflation as well as simple and inexpensive manufacturing and installation. The configuration of the inflator 24 will be described in greater detail in connection with Figure 2.

Referring to Figure 2, a side elevation, cross sectional view of the inflator 24 is shown. The inflator 24 may have a gas chamber 54 formed of a material with a comparatively high tensile strength, such as steel. The gas chamber 54 may be formed of a single, unitary piece. In the alternative, the gas chamber 54 may be made from multiple pieces that are welded or otherwise attached together to provide the configuration shown in Figure 2. The gas chamber 54 may have a generally tubular shape.

The inflator 24 may be positioned within a first inlet port 60 of the first protection zone 40 and a second inlet port 62 of the second protection zone 42 so that inflation gas leaving the gas chamber 54 directly enters the first and second protection zones 40,42.

Hence, a gas conduit is not required to channel the inflation gas from the inflator 24 to the inflatable curtain 10. The inflator 24 may simply be clamped in gas-tight fashion within the first and second inlet ports 60,62, for example, through the use of ring-shaped clamps 64 that tightly press the fabric of the inlet ports 60,62 against the surface of the inflator 24.

The dimensions of the gas chamber 54 may be varied to suit the volume in which the gas chamber 54 is to be installed. For example, the gas chamber 54 may be made longer than shown in the longitudinal direction 13 and/or thinner in the lateral and transverse directions 14,15 to facilitate installation in a long, narrow space such as the space beside the roof rail 36. A longer gas chamber 54 may be installed such that the gas chamber 54 extends a significant distance into each protection zone 40,42. Such installation may advantageously provide inflation gas flows that enter the inflatable curtain 10 about midway through each of the protection zones 40,42 for more even inflation.

The gas chamber 54 may have a first end 66 disposed proximate the first inlet port 60 and a second end 68 disposed proximate the second inlet port 62. The first end 66 may have a first exit orifice 70, and the second end 68 may have a second exit orifice 72. Each of the first and second exit orifices 70,72 has an open configuration, in which inflation gas can pass relatively freely through the exit orifices 70,72, and a sealed configuration, in which substantially all inflation gasses are trapped within the gas chamber 54. <BR> <BR> <P>Consequently, in this application, "exit orifice"refers to more than just a passageway; the structure that provides selective closure of the passageway is also included.

More precisely, each of the exit orifices 70,72 may include a diffuser 74, which takes the form of a cap that seals the corresponding end 66 or 68 of the gas chamber 54.

The diffusers 74 may each be unitary with the tubular body of the inflator 24, or may be separate caps that are welded or otherwise affixed to the body of the inflator 24. Each diffuser 74 may have an opening 76 against which a burst disc 78 is pressed by the pressure within the gas chamber 54. The burst discs 78 may have a wide variety of configurations; if desired, each of the burst discs 78 may have a slightly domed shape to provide a tight seal with the circular shape of the associated opening 76.

The burst discs 78 are preferably shaped to deflect under a pressure increase to uncover the openings 76. For example, the burst discs 78 may be made to bend enough to fit through the openings 76, so that the pressure increase ejects the burst discs 78 from the openings 76. The burst discs 78 may simply have a pressure threshold above which sufficient deformation occurs to push the burst discs 78 through the openings 76.

Alternatively, the burst discs 78 may deform primarily in response to shock, or rapid pressure changes within the gas chamber 54.

Each of the openings 76 may have a counterbored shape with the larger portion disposed inward, toward the burst disc 78, and the narrower portion disposed outward.

The larger portion may be sized to promote deflection and passage of the burst disc 78 through the opening 76 when the proper pressure or shock is achieved within the gas chamber 54. The narrower portion may serve as a flow restrictor to meter the flow of inflation gas from the opening 76. Depending on the configuration of the burst disc 78, the desired flow rate of inflation gas upon deployment, and other factors, the larger and narrower portions may be switched such that the larger portion is inwardly disposed and the smaller portion is outwardly disposed. Alternatively, the counterbore may be eliminated entirely in favor of an opening 76 of uniform diameter.

In order to prevent the ejected burst discs from damaging the inflatable curtain 10, the inflator 24 may also have a pair of burst disc retention members 90, each of which is disposed outside one of the exit orifices 70,72. The burst disc retention members 90 may have a wide variety of configurations. As illustrated, the burst disc retention members 90 may take the form of cylindrical screens, through which inflation gases pass relatively freely. The screens may be formed of a mesh material, which may, for example, be obtained from the Metex Corporation of Edison, New Jersey. The burst discs 78 are simply captured by the burst disc retention members 90 after ejection from the openings 76. The burst discs 78 may remain in front of the openings 76, in which case inflation gases must simply flow around the burst discs 78 to exit the inflator 24.

The inflator 24 may also have a pair of gas guide diffusers 92 disposed outside the exit orifices 70,72 and the burst disc retention members 90. Upon deployment of the inflator 24, a first gas flow 94 may exit the gas chamber 54 via the first exit orifice 70, and a second gas flow 96 may exit the gas chamber 54 via the second exit orifice 72. Each of the gas flows 94,96 may then travel through the associated gas guide diffuser 92 to reach the corresponding inlet port 60,62 of the inflatable curtain 10.

Each of the gas guide diffusers 92 may have a throat 93 that acts to retain the associated burst disc retention member 90. The throats 93 may also act as exit nozzles to pace the flow of inflation gas from the inflator 24. The throats 93 may be formed, for example, by crimping or otherwise compressing the generally tubular shapes of the gas guide diffusers 92.

As shown, the first and second gas flows 94,96 travel in the longitudinal direction 13, along the longitudinal axis of the inflator 24. Provided the first and second gas flows 94,96 are equal in momentum, i. e. , the gas flows 94,96 have an equal mass flow rate and an equal exit velocity, the thrust produced by each of the gas flows 94,96 will neutralize that of the other. Hence, the inflator 24 will be subject to substantially no thrust in the longitudinal direction 13.

As a result, the inflator 24 may be attached to the vehicle 12 with only minimal support against axial motion of the inflator 24, or motion in the longitudinal direction 13.

For example, the mounting brackets 26 depicted in Figure 1 interfere directly with motion of the inflator 24 in the lateral and transverse directions 14,15, but provide only frictional support against motion in the longitudinal direction 13. Such frictional support may be sufficient when a substantially thrust-neutral design, like that of Figure 2, is utilized.

The inflator 24 may be comparatively easily installed in the vehicle 12 to obtain the configuration depicted in Figure 1. For example, the gas guide diffuser 92 proximate the first end 66 of the gas chamber 54 may be inserted into the first inlet port 60, and the gas guide diffuser 92 proximate the second end 68 may be inserted into the second inlet port 62. The inflatable curtain 10 may then be attached to the roof rail 36 in the position shown in Figure 1, and the inflator 24 may be attached to the roof rail 36 with the mounting brackets 26. The steps described above may be reordered in many ways to suit the particular configuration of the vehicle 12; for example, the inflator 24 may first be attached to the roof rail 36 with the mounting brackets 26, and the inlet ports 60,62 may then be fitted around the gas guide diffusers 92. The inflatable cushion 10 may then be fixed in place.

Dual flow inflators according to the invention may alternatively be made in a non- thrust-neutral manner. For example, the openings 76 and/or the gas guide diffusers 92 of the first and second ends 66,68 need not be equal in size, but may be sized differently to provide varying amounts of inflation gas. Such unequal flows may be desirable, for example, if the first and second protection zones 40,42 were sized differently. In such a case, the thrust from one of the gas flows 94,96 may only partially negate that of the other gas flow 94 or 96. Varying degrees of longitudinal support may be provided to account for such inequalities in thrust.

The gas guide diffusers 92 are optional; inflation gases may simply be allowed to freely escape the inflator 24 after traveling through the burst disc retention members 90.

However, the gas guide diffusers 92 may beneficially provide more accurate direction of the first and second gas flows 94,96, and hence more accurate direction of the thrust exerted by the escaping inflation gases on the inflator 24. The gas guide diffusers 92 may also increase the speed with which the first and second gas flows 94,96 escape the inflator 24, so that the gas flows 94,96 have the momentum to travel further into the inflatable curtain 24. Such rapid ejection may help to ensure that the portions of the inflatable curtain 10 that are furthest from the inflator 24 are adequately inflated prior to impact of the person against the inflatable curtain 10.

A dual flow inflator may be activated in a variety of ways to inflate the inflatable curtain 10. According to one embodiment, the first and second gas flows 94,96 may both be triggered by the action of a single initiation assembly 100. The initiation assembly 100 may be affixed to one side of the inflator 24, and may communicate with the gas chamber

54 through an initiator aperture 102 of the gas chamber 54. The initiation assembly 100 may be disposed almost entirely outside the gas chamber 54.

The initiation assembly 100 may, for example, be laser welded in place to prevent the escape of inflation gases through the initiator aperture 102 or ejection of the initiation assembly 100 during deployment of the inflator 24. The initiation assembly 100 may be positioned halfway between the first and second exit orifices 70,72 to ensure that the first and second gas flows 94,96 are generated and expelled substantially simultaneously.

The initiation assembly 100 may have an initiator 104, which is an electrically- triggered pyrotechnic device. The initiator 104 may, for example, have a head 106 that contains pyrotechnic material, a body 108, and electrical prongs 110 through which the activation signal is received. The body 108 may be seated within an initiator receptacle 111, and may be held in place through the use of an initiator retention member 112. An o- ring 113 may be used to form a substantial seal between the initiator 104 and the initiator receptacle 111. The prongs 110 may be inserted into a plug 114 of the electric line 22 leading to the accelerometer 20.

A burst disc 115 may be disposed on the initiator receptacle 111, within the gas chamber 54, to seal the initiator 104 from the interior of the gas chamber 54 until the inflator 24 has deployed. Upon deployment of the initiator 104, the burst disc 115 may be removed to expose the initiator 104 to the interior of the gas chamber 54.

The inflator 24 may have a fill port 116 through which gaseous, liquid, or even solid material can be inserted into the gas chamber 54. The fill port may be salable through the use of a stopper 118, which may take the form of a metallic bead that can be pressed into the fill port 116 and welded in place.

The inflator 24 may be of any type, including pyrotechnic, compressed gas, and hybrid types. In the embodiment of Figure 2, the inflator 24 may contain a gas-producing material 121 in a compressed state. The gas-producing material 121 may be substantially <BR> <BR> inert, i. e. , non-reactive at the temperatures and pressures that occur during activation of the inflator 24. Due to the compression, a portion of the gas-producing material 121 may be in liquid form within the gas chamber 54.

Alternatively, the inflator 24 may be a pyrotechnic inflator, so that the gas- producing material 121 is not an inert compressed liquid, gas, or mixture, but takes the form of a combustible solid, gas, or liquid. The inflator 24 may also be a hybrid inflator,

in which case the gas-producing material 121 may include both inert and pyrotechnic components.

With the inert, compressed, gas-producing material 121 of Figure 2, the initiation assembly 100 deploys within milliseconds to produce heat that causes expansion of the gas-producing material 121. The result is a sudden pressure increase within the gas chamber 54. The pressure increase, or possibly just the shock wave induced by deployment of the initiator 104, dislodges the burst discs 78 to open the first and second exit orifices 70,72. As the gaseous portion of the gas-producing material 121 flows out of the inflator 24, the liquid is vaporized to add to the volume of the first and second gas flows 94,96. Thus, a considerable amount of gas can be produced by the inflator 24, despite its modest size.

Furthermore, the presence of a portion of the gas-producing material 121 in liquid form may be beneficial because the liquid will absorb heat as it vaporizes. Hence, the first and second gas flows 94,96 will be comparatively cool, and therefore less likely to damage the inflatable curtain 10. The inflatable curtain 10 may therefore be made from a comparatively less heat-resistant and quite possibly cheaper material. For example, a thinner silicon coating for the fabric of the inflatable curtain 10 may be sufficient to protect the fabric from thermal damage.

The inflator 24 is comparatively inexpensive and easy to manufacture. According to one manufacturing method, the gas chamber 24 may first be formed through known methods. If desired, the gas chamber 24 may be provided as a single unitary piece, as depicted in Figure 2. The gas-producing material 121 may be inserted through the fill port 116 prior to installation of the stopper 118. In the alternative, the gas-producing material may be cryogenically processed, i. e. , frozen and compressed into solid form, and inserted through the initiator aperture 102 prior to installation of the initiation assembly 100. The initiation assembly 100 may be welded or otherwise firmly fixed in place to avoid escape of the gas-producing material 121 from the gas chamber 54.

In the alternative to one-piece construction, the gas chamber 54 may be formed as two separate pieces to facilitate the insertion of the burst discs 78, the initiation assembly 100, and the gas-producing material 121. For example, the first end 66 may be separated from the remainder of the gas chamber 54 by a radial seam (not shown), so that each of the first end 66 and the remainder of the gas chamber 54 forms a tube with a circular opening.

The burst discs 78, the initiation assembly 100, and/or cryogenic material may easily be

inserted into such circular openings and fixed in place. The first end 66 may then be attached, for example, through welding, to the remainder of the gas chamber 54.

Many other aspects of the inflator 24 may be varied to suit the geometry of the vehicle 12, the size and shape of the inflatable curtain 10, and the available manufacturing equipment. Figures 3 through 5 present alternative embodiments of dual flow inflators, each of which contains a number of variations from the inflator 24 of Figure 2. These variations may be used in any combination, or in conjunction with other variations that will be recognized by those of skill in the art, to produce a larger number of embodiments of the invention than can be illustrated or specifically described herein.

Referring to Figure 3, an inflator 124 according to one alternative embodiment of the invention is shown. The inflator 124 may have a gas chamber 154, and may be designed to be installed within inflation ports of an inflatable curtain, in much the same manner as the gas chamber 54 of Figure 2. The inflation ports and attachment features have been omitted from Figure 3 for clarity.

The gas chamber 154 of Figure 3 may have a multi-part configuration designed for easy manufacturing and installation. More specifically, the gas chamber 154 may have a first vessel 156 and a second vessel 158, each of which has a generally tubular configuration. Additionally, the gas chamber 154 may have a bulkhead 159 that also has a generally tubular configuration. Each of the vessels 156,158 may have an interior end 160 an exterior end 161. The exterior ends 161 may be closed, with a flat circular, hemispherical, or otherwise dome-like configuration. By contrast, the interior end 160 of the first vessel 156 may have a first interior opening 162, and the interior end 160 of the second vessel 158 may have a second interior opening 163.

The bulkhead 159 may have a first aperture 164 shaped to match the interior end 160 of the first vessel 156 and a second aperture 165 shaped to match the interior end 160 of the second vessel 158. Preferably, the first and second apertures 164,165 can be aligned with the interior ends 160 in such a manner that fluids can pass relatively freely between the first vessel 156, the second vessel 158, and the bulkhead 159. For example, the first and second apertures 164,165 may be sized approximately the same as the inside diameters of the interior ends 160 so that the interior ends 160 can abut the apertures 164, 165 to form a continuous tubular shape.

As shown in Figure 3, inertial welding may been used to affix the interior ends 160 to the bulkhead 169. More specifically, the first and second vessels 156,158 may be spun

with a desired rotational inertia and pressed against the bulkhead 159 to frictionally weld the interior ends 160 to the bulkhead 169, thereby curling the interior ends 160 somewhat.

If desired, the apertures 164,165 may also be sized to contain the interior ends 160, in which case a weld, interference fit, or the like may be used to keep the interior ends 160 seated firmly within the apertures 164,165.

When assembled, the first and second vessels 156,158 and the bulkhead 159 form the gas chamber 154. The gas chamber 154 may have a first end 166 located on the first vessel 156 and a second end 168 located on the second vessel 158. A first exit orifice 170 may be positioned on the first end 166, and a second exit orifice 172 may be positioned on the second end 168.

Like the exit orifices 70,72 of Figure 2, each of the exit orifices 170,172 has an open configuration that permits gas flow and a sealed configuration, in which gas cannot escape through the exit orifices 170,172. However, in place of the burst discs 78 and openings 76 of the inflator 24 of Figure 1, each of the exit orifices 170,172 may take the form of a frangible surface such as a scored surface 170,172. Each of the scored surfaces 170,172 has a first deformable portion 174, a second deformable portion 176, and a weakened region 178.

The weakened region 178 may take the form of a score 178 formed in the surface of the first end 166. The score 178 may be formed by gouging the first end 166, for example, with a sharpened tool constructed of hard steel, tungsten carbide, diamond, or the like. The tool may be shaped to peel off a layer of the material of the first end 166; multiple operations may be used to remove the desired amount of material.

The scores 178 may take a wide variety of configurations. For example, each score 178 may simply comprise a single line disposed within the plane perpendicular to the transverse direction 15. Alternatively, a star-like shape with multiple intersecting scores (not shown) may be used. The following description assumes the use of a single line for each score 178, as depicted in Figure 3. With a star-like shape, operation of the scores would be similar to that of the scores 178 of Figure 3. Multiple wedge-shaped deformable portions would exist between the intersecting scores; each deformable portion would bend or"bloom"outward upon failure of the scores.

The depth of the score 178 should be selected such that the score 178 ruptures when the pressure within the gas chamber 154 reaches a predetermined threshold, or when the pressure shock within the gas chamber 154 reaches a predetermined threshold. A

deeper score would produce an exit orifice 166 or 168 that opens in response to a lower pressure or shock. The scores 178 of the first and second scored surfaces 170,172 may be an equal depth to ensure that the first and second scored surfaces 170,172 open simultaneously, and that thrust neutrality is maintained. In the alternative, the scores 178 of the first and second scored surfaces 170,172 may be varied in depth, length, width, or configuration to provide different timing and/or gas flow characteristics.

The first and second deformable portions 174,176 may be first and second lips 174,176 that are integrally formed with each other, on either side of the scores 178.

When the scores 178 rupture, the lips 174,176 may deflect outward somewhat to reach a deformed configuration 180, shown in phantom. In the deformed configuration 180, the lips 174,176 are separated somewhat to provide an opening through which inflation gas can escape.

Indeed, in the deformed configuration 180, the lips 174,176 perform the functions accomplished by the openings 76 and the gas guide diffusers 92 of Figure 2. The lips 174, 176 may be configured to deflect such that an opening of the desired size is produced. For example, in order to form a larger opening, the lips 174,176 may be made somewhat thinner than the surrounding portions of the vessels 156,158. Alternatively, the lips 174, 176 may be notched, thermally treated, or otherwise processed to control the amount of deflection present in the deformed configuration 180, and hence, the size of the opening through which inflation gas flows.

In order to ensure that the first and second scored surfaces 170,172 are opened completely and simultaneously, a first piston 190 may be disposed within the first vessel 156, and a second piston 192 may be disposed within the second vessel 158. Each of the pistons 190,192 may have a generally cylindrical shape that engages the interior diameter of the associated vessel 156,158 to restrict fluid passage across the pistons 190,192. The pistons 190,192 need not form a hermetic seal with the vessels 156,158 ; rather, the pistons 190,192 simply restrict fluid flow through the space between the pistons 190,192 and the vessels 156,158.

The inflator 124 may have an initiation assembly 200 installed in a manner similar to that of the initiation assembly 100 of Figure 2. The initiation assembly 200 may be seated within an initiator aperture 102 formed in the bulkhead 159, and may be disposed almost entirely outside the bulkhead 159. Gas-producing material 121 may be stored within the gas chamber 154, as in Figure 2. Of course, the gas-producing material 121

may include gaseous and/or liquid components, or may instead include a pyrotechnic material.

If desired, the initiation assembly 200 may be configured somewhat differently from the initiation assembly 100 of the previous embodiment. More specifically, the initiation assembly 200 may have an initiator 204 with a head 206, a body 108, and prongs 110 that receive an ignition signal. The initiator 200 may be retained by an initiator receptacle 211 and an initiator retention member 212. An o-ring 213 may form a substantially gas-tight seal between the initiator receptacle 211 and the initiator retention member 212.

The initiator receptacle 211 may have an enlarged interior cavity to contain a quantity of booster material 216, which may be disposed about the head 206. A dome 218 may encapsulate the booster material 216 and keep the booster material 216 in a comparatively tight arrangement about the head 206. Upon activation of the initiator 204, the booster material 216 may also ignite to intensify the thermal energy provided by the initiator 204. The dome 218 may be designed to rupture, or even disintegrate, upon activation of the initiator 204.

When the initiation assembly 200 deploys, the gas-producing material 121 between the pistons 190,192 expands and presses the pistons 190,192 outward, in the directions indicated by the arrows 194. The gas-producing material 121 between the first piston 190 and the first scored surface 170 and between the second piston 192 and the second scored surface 172 initially receives a comparatively smaller quantity of heat from the initiation assembly 200. Consequently, the pistons 190,192 are driven outward, toward the scored surfaces 170,172. As the pistons 190,192 move, the gas-producing material 121 outside the pistons 190,192 is compressed. The pressure increase and/or shock ruptures the scores 178 and presses the lips 174,176 into the deformed configuration 180, thereby opening the scored surfaces 170,172.

If one of the scored surfaces 170,172 opens prior to the other, the pistons 190,192 may ensure that sufficient pressure remains within the gas chamber 154 to open the remaining scored surface 170 or 172. More specifically, the tight fit of the pistons 190, 192 within the vessels 156,158 limits the rate at which inflation gas is able to escape from between the pistons 190,192. Hence, even when the pressure outside one of the pistons 190,192 decreases in response to the rupture of the adjacent scored surface 170 or 172,

gas continues to press the pistons 190,192 outward to ensure that the remaining scored surface 170 or 172 is ruptured.

Furthermore, the pistons 190,192 may generally restrict the rate at which inflation gases are able to escape the gas chamber 154. Thus, the pistons 190,192 may also perform a part of the function carried out by the gas guide diffusers 92. Restriction of the <BR> <BR> flow rate of the inflation gases may help to prevent"bag slap, "or injury to vehicle occupants as a result to overly rapid inflation of the inflatable curtain 10. Furthermore, the pistons 190,192 may ensure that inflation gases are supplied to the inflatable curtain 10 over a long enough time period to keep the inflatable curtain 10 inflated during a prolonged accident such as a rollover.

The use of the pistons 190,192 is optional; the inflator 124 may be configured to operate reliably without them. For example, through somewhat tight tolerancing of dimensions of the scores 178 or through the use of other pressure regulating mechanisms, full and substantially simultaneous opening of the first and second scored surfaces 170, 172 may be ensured.

The inflator 124 may be comparatively easily manufactured. The vessels 156,158 may be initially separate from the bulkhead 159. The exterior ends 161 of the vessels 156, 158 may be scored through the use of an appropriate tool, as described above. Although the scores 178 are disposed on the outsides of the vessels 156,158 in Figure 3, scores may be formed on the interior surfaces of the vessels 156,158, in the alternative or in addition to the scores 178 on the outsides.

The pistons 190,192 and the gas-producing material 121 may then be easily inserted into the interior openings 162,163 of the vessels 156,158. Again, cryogenic methods may be used to compact the gas-producing material 121. Similarly, the apertures 164,165 may aid in the installation and positioning of the initiation assembly 200 within the initiator aperture 102 of the bulkhead 159. After the gas-producing material 121, the pistons 190,192, and the initiation assembly 200 have been installed, the interior ends 160 of the first and second vessels 156,158 may be affixed to the bulkhead 159 in alignment with the first and second apertures 164,165.

The vessels 156,158 may be fixed in place within the bulkhead 159, for example, through the use of a method such as inertial welding. More specifically, as mentioned previously, the vessels 156,158 may be rotated rapidly around the longitudinal axis 13, pressed against the bulkhead 159 in alignment with the apertures 164,165, and permitted

to stop rotating. The heat generated by frictional engagement of the interior ends 160 with the bulkhead 159 forms a weld between the vessels 156,158 and the bulkhead 159.

Referring to Figure 4, an inflator 224 according to another alternative embodiment of the invention is shown. The inflator 224 may have a gas chamber 254 and may be designed to be installed within inflation ports of an inflatable curtain, in much the same manner as the inflator 24 of Figure 2. The inflation ports and attachment features have been omitted from Figure 4 for clarity.

Like the gas chamber 154 of Figure 3, the gas chamber 254 of Figure 4 may have a multi-part configuration. The gas chamber 254 may have a first vessel 256 and a second vessel 258, each of which has a generally tubular configuration. Additionally, the gas chamber 154 may have a bulkhead 259 that has a generally spherical, rather than tubular, shape.

The spherical shape may permit the bulkhead 259 to hold a larger quantity of gas- producing material 121. Thus, the inflator 224 may be used to provide additional inflation gas, or in the alternative, the vessels 256,258 may be made somewhat smaller because they need not hold the same quantity of gas-producing material. Hence, the choice of whether a spherical or tubular bulkhead is desired depends on the needed quantity of inflation gas as well as the space available for the inflator.

Like the vessels 156,158 of Figure 3, each of the vessels 256,258 may have an interior end 260 an exterior end 261. The exterior ends 261 may be closed, with a flat circular, hemispherical, or otherwise dome-like configuration. The interior end 260 of the first vessel 256 may have a first interior opening 262, and the interior end 260 of the second vessel 258 may have a second interior opening 263.

Similarly, the bulkhead 259 may have a first aperture 264 that receives the interior end 260 of the first vessel 256 and a second aperture 265 that receives the interior end 260 of the second vessel 258. The gas chamber 254 may have a first end 266 and a second end 268; a first exit orifice 270 may be positioned at the first end 266 and a second exit orifice 272 may be positioned at the second end 268. Like the exit orifices 70,72 of Figure 2 and the exit orifices 170,172 of Figure 3, the exit orifices 270,272 may be frangible structures. However, instead of burst discs or scored surfaces, the exit orifices 270,272 may take the form of compression closures.

A"compression closure"may be defined as an opening that has been closed, or nearly closed, through mechanical deformation of the material surrounding the opening.

Thus, compression closures include openings that have been crimped, swaged, twisted, folded, or otherwise deformed into a closed position.

As shown in Figure 4, the first and second exit orifices 270,272 take the form of crimped openings 270,272, or closures formed through the simple application of mechanical compression perpendicular to the axis of the opening. More particularly, each of the crimped openings 270,272 may have a first deformable portion 274, a second deformable portion 276, and a weakened region 278.

The first and second deformable portions 274,276 may take the form of lips 274, 276, somewhat similar to the lips 174,176 of the previous embodiment. However, rather than being formed integrally in a closed position, the lips 274,276 may be formed in an open position and closed in a subsequent crimping operation. The lips 274,276 may, more specifically, be pressed together in the transverse direction 15. The weakened region 278 may take the form of a weld 278 used to hold the lips 274,276 together and ensure that they are sealed.

In a manner similar to the previous embodiment, the weld 278 may rupture in response to a high pressure and/or pressure shock within the gas chamber 254. The lips 274,276 may then open into the deformed configuration 280, shown in phantom, to permit inflation gas to escape the gas chamber 254. The compressive force applied to close the lips 274,276 and the weld strength of the weld 278 may be selected to obtain a desired threshold pressure or shock. The compressive force and the weld strength may be toleranced somewhat tightly to ensure that the first and second crimped openings 270,272 open substantially simultaneously.

The inflator 224 may have a first piston 290 and a second piston 292 disposed within the first and second vessels 256,258 in a manner similar to the pistons 190,192 of the previous embodiment. An initiation assembly 300 somewhat similar to that of Figure 2 may be seated within an initiator aperture 102 of the bulkhead 259 to induce a rapid pressure rise between the pistons 290,292. The initiation assembly 300 may differ from the initiation assembly 100 in that an initiator receptacle 311 of the initiation assembly 300 is shaped to fit partially within the bulkhead 259. Thus, the initiation assembly 300 protrudes from the bulkhead 259 by a comparatively smaller distance.

Like the pistons 190,192, the pistons 290,292 move outward, in the directions indicated by the arrows 294, upon activation of the initiation assembly 300. However, the pistons 290,292 may be configured somewhat differently than the pistons 190,192. More

specifically, the first piston 290 may have a first puncture member 296, and the second piston 292 may have a second puncture member 298. The puncture members 296,298 may be designed to physically contact the crimped openings 270,272 when the pistons 290,292 move to ensure that the crimped openings 270,272 open completely.

The puncture members 296,298 may each have a sharpened tip 299 that is inserted between the lips 274,276 to wedge the lips 274,276 apart, thereby inducing rupture of the welds 278. Further motion of the sharpened tips 299 through the crimped openings 270, 272 may spread the lips 274,276 apart by a distance selected to permit the desired flow rate of inflation gas to flow through the crimped openings 270,272. As with the previous embodiment, inflation gas may escape form between the pistons 290,292 at a somewhat slower rate to flow out of the gas chamber 254 through the crimped openings 270,272.

The inflator 224 may be manufactured in a manner similar to that of the inflator 124. More specifically, the vessels 256,258 may be manufactured separately from the bulkhead 259. The exterior ends 261 of the vessels 256,258 may initially be open, and may be pressed together through a crimping process carried out with the aid of a hydraulic press or the like.

The pistons 290,292 and the gas-producing material 121 may then be inserted into the interior openings 262,263 of the vessels 256,258. Again, cryogenic methods may be used to compact the gas-producing material 121. The initiation assembly 300 may be installed in the initiator aperture 102 of the bulkhead 259. According to one example, the initiation assembly 300 may be welded in place via welds 317, as shown in Figure 4.

After the gas-producing material 121, the pistons 290,292, and the initiation assembly 400 have been installed, the interior ends 260 of the first and second vessels 256, 258 may be inserted into the first and second apertures 264,265 of the bulkhead 259 and fixed in place with a method such as welding or interference fitting. In the exemplary embodiment of Figure 4, welds 319 have been used to fix the interior ends 260 of the vessels 256,258 in place within the bulkhead 259.

Referring to Figure 5, an inflator 324 according to yet another alternative embodiment of the invention is shown. The inflator 324 may have a gas chamber 354 with a generally spherical shape. The gas chamber 354 may be installed within inflation ports of an inflatable curtain, in much the same manner as the inflators 54,154, 254 of previous embodiments. In place of the clamps 64, some attachment mechanism (not shown) designed to connect the inlet ports 60,62 to a spherical, rather than cylindrical,

object may be used. In the alternative, the inflator 324 may be attached in an entirely different position than the position of the inflator 24 in Figure 1. The inflator 324 may, for example, be readily used for front impact airbags positioned on the driver's side or the passenger's side.

The gas chamber 354 may have a first hemispherical portion 356 and a second hemispherical portion 358. The first and second hemispherical portions 356,358 may be attached together at an equatorial region 360. The first and second hemispherical portions 356,358 may, for example, be attached by fastening, welding, or the like. A mounting flange 362 may extend outward from the equatorial region 362. The mounting flange 362 may be integrally formed with the second hemispherical portion 358 as shown, or may be disposed on both hemispherical portions 356,358, or may be a separate piece attached to the hemispherical portions 356,358 at the equatorial region 360.

The mounting flange 362 may be used in place of the mounting brackets 26 to attach the inflator 324 to the vehicle 12. The mounting flange 362 may have a plurality of mounting holes 364 arrayed around its circumference so that fasteners (not shown) can be inserted through the mounting holes 364 and through aligned holes of a similar flange within the vehicle 12. Additionally or in the alternative, the mounting flange 362 may be used to affix the inlet ports 60,62 to the inflator 324; external ring clamps or the like may be used to facilitate such attachment. As another alternative, the mounting flange 362 may be omitted entirely in favor of other forms of vehicle and/or inlet port attachment.

As with previous embodiments, the gas chamber 354 may have a first end 366 and a second end 368 disposed opposite the first end 366. Of course, in the embodiment of Figure 5, the first and second ends 366,368 are not disposed at the end of any tubular structure, but on opposite sides of the spherical shape of the gas chamber 354. The first end 366 may have a first exit orifice 370, and the second end 368 may have a second exit orifice 372. The first and second exit orifices 370,372 may each have an open configuration that permits gas flow and a closed configuration that keeps gases from leaving the gas chamber 354.

The first and second exit orifices 370,372 may be configured in a manner somewhat similar to the exit orifices 70,72 of Figure 2. More particularly, the first and second exit orifices 370,372 may each have an opening 376 and a burst disc 378 that blocks the opening 376 in the closed configuration. As with the burst discs 78, the burst

discs 378 may deflect in response to high pressure and/or pressure shock, and may then be ejected from the openings 376.

Burst disc retention members 390 may be positioned outward of the openings 376 to capture the burst discs 378 to prevent damage to the inflatable curtain 10. The burst disc retention members 390 may take the form of dome or plateau-shaped flanges with holes to permit gas flow through the burst disc retention members 390. In the alternative, the burst disc retention members 390 may have a mesh structure like that of the burst disc retention members 90 of Figure 2.

As with the previous embodiments, the inflator 324 may have an initiator assembly 300 like that of the previous embodiment. The initiator assembly 300 may be positioned at the equatorial region 360, or may be located off-center as shown in Figure 5 to avoid interference with the attachment of the first and second hemispherical portions 356,358.

In such a case, the initiation assembly 300 may be installed within an initiator aperture 102 of the first hemispherical portion 356. If desired, the initiator receptacle 311 of the initiation assembly 300 may be elongated somewhat to position the initiator 104 near the center of the gas chamber 354 to ensure that deployment of the initiator 104 causes substantially simultaneous opening of the first and second exit ports 370,372.

As with previous embodiments, the gas-producing material 121 contained by the inflator 324 may include a gas and/or a liquid. Alternatively, a pyrotechnic material could be used. The initiation assembly 300 may heat the gas-producing material 121 to increase the pressure within the gas chamber 354. The first and second exit ports 370,372 may open in response to the pressure increase, thereby inflating the inflatable curtain 10 in a manner similar to that of the inflator 24 of Figure 2.

The inflator 324 may also be manufactured comparatively easily. The first and second hemispherical portions 356,358 may first be formed through methods known in the art. The burst disc retention members 390 may be attached, for example, by welding, to the first and second ends 366,368. The burst discs 378, the initiation assembly 300, and the gas-producing material 121 may then be installed via the open ends of the hemispherical portions 356,358. If desired, the gas-producing material 121 may be inserted in cryogenic form.

As with the previous embodiment, the initiation assembly 300 may be attached to the first hemispherical portion via welds 317. The first and second hemispherical portions

356,358 may then be attached together, for example, through a method such as welding, brazing, or mechanical fastening.

Referring to Figure 6, an inflatable curtain 410 according to one embodiment of the invention is shown installed in a vehicle 412. The inflatable curtain 410 may form part of an airbag system configured to protect one or more vehicle occupants against lateral impact through the formation of a protective curtain beside the occupants.

The vehicle 412 has a longitudinal direction 413, a lateral direction 414, and a transverse direction 415. The vehicle 412 further has front seats 416 laterally displaced from first lateral surfaces 417, or front doors 417, as shown in the vehicle 412 of Figure 6.

The vehicle 412 also has rear seats 418 laterally displaced from second lateral surfaces 419, or rear doors 419, as depicted. As shown, two such inflatable curtains 410 may be used: one for the driver's side of the vehicle 412, and the other for the passenger's side.

The two inflatable curtains 410 may or may not be the same volume or size.

The inflators 424 and the inflatable curtains 410 may be attached to roof rails 436 of the vehicle 412. Depending on the model of the vehicle 412 and the desired configuration of the inflatable curtains 410, airbag components may also be disposed along the B pillars 437, C pillars 438, and/or D pillars 439.

The inflatable curtains 410 shown in Figure 6 are configured to protect not only occupants of the front seats 416, but those of the rear seats 418 as well. Thus, each inflatable curtain 410 may have a volume 440 that is configured to inflate between the front seats 416 and one of the front doors 417, and a second volume 442 configured to inflate between the rear seats 418 and one of the rear doors 419. The first and second volumes 440,442 of the inflatable curtain 410 may define protective zones within an automobile, where the protective zones are established to attenuate the motion of an automobile passenger.

The first and second volumes 440,442 may be parts of the same inflatable curtain, <BR> <BR> i. e. , the first and second volumes 440,442 are in fluid communication with each other, even when gas is not able to flow through the inflator 424 between the first and second volumes 440,442. However, the inflatable curtains 410 may optionally be adapted to have multiple inflatable curtains 410 that are isolated from each other.

Furthermore, the individual inflatable curtain volumes 440,442 may have varying sizes and capacities according to the various automobile applications. The size and

volume 440,442 of the inflatable curtains 410 will be a function of the size of the protected zone in which they are located.

The first and second volumes 440,442 of each inflatable curtain 410 may be attached together through the use of a connection zone 444 positioned between the volumes 440,442. The connection zone 444 may provide a flow path through which gases can flow between the first and second volumes 440,442.

Each of the inflatable curtains 410 may have a front tether 446 attached to the A pillar 434 and a rear tether 448 attached to the roof rail 436 to exert tension on the inflatable curtains 410 to keep them in place during inflation and impact. Those of skill in the art will recognize that the tethers 446,448 may also be attached to other parts of the vehicle 412, such as the B pillars 437, C pillars 438, and/or D pillars 439. The tethers 446, 448 may be constructed of standard seatbelt webbing or the like.

Although each inflatable curtain 410 illustrated in Figure 6 has two volumes 440, 442, the invention encompasses the use of inflatable curtains 410 with any number of inflatable curtain volumes 440,442. Thus, if desired, each of the inflatable curtains 410 may be extended to have one or more protective zones positioned to protect occupants of extra seats 550 behind the rear seats 418 from impact against the third lateral surfaces 452 of the vehicle 412. Additional inflators 424 may be used to inflate such additional inflatable curtain volumes.

The inflators 424 may take the form of a hollow pressure vessel containing a gas generant, such as chemically reactive material and/or compressed gas. The inflator 424 can be activated and gas released upon application of electricity to an initiator which initiates an outflow of inflation gases from the inflator. In the exemplary configuration of Figure 6, the inflators 424 are partially enveloped within the inflatable curtains 410 so that inflation gases exiting the inflators 424 flow directly into the inflatable curtains 410. The inflators 424 may operate with such rapidity that, before the vehicle 412 has fully reacted to the impact, the inflatable curtains 410 have inflated to protect vehicle occupants from impact.

The inflators 424 may be uniquely configured to provide even and rapid inflation, as well as simple and inexpensive manufacturing and installation. The configuration of the inflator 424 will be described in greater detail with reference to Figure 7.

Referring to Figure 7, a cross-sectional view of the inflator 424 is shown. The inflator 424 may have a gas chamber 454 formed of a material with a comparatively high

tensile strength, such as steel. The gas chamber 454 may be formed of a single, unitary piece. In the alternative, the gas chamber 454 may be made from multiple pieces that are welded or otherwise attached together to provide the configuration shown in Figure 7.

The gas chamber 454 may have a generally tubular shape that includes flat, hemispherical, or otherwise dome-like caps.

The inflator 424 comprises a first orifice 470 and a second orifice 472. The first and second orifices 470,472 provide a channel by which the gas within the gas chamber 454 may exit the inflator 424. In the inflator 424 illustrated in Figure 7, the first orifice 470 and the second orifice 472 are both comprised of two sections: an ejection orifice 480, 482 and a retention orifice 484,486.

The two different sections of the orifices 470,472 are distinguished because of their individual functions. In some embodiments, the ejection orifices 480,482 are separately sized and adjusted from the retention orifices 484,486 depending upon the individual applications. Generally, the retention orifices 484,486 provide a location to support the gas retention mechanisms, such as burst disks 478. In an inflator 424 having burst disks 478, the retention orifices 484,486 would be opened once the burst disks 478 are forced through the orifices 470,472. The retention orifices 484,486 may be similarly sized, or may alternatively be different sizes depending upon the retention mechanisms.

The ejection orifices 480,482 are generally positioned outward from the retention orifices 484,486, such that gas ejecting from the gas chamber 454 will first pass through the retention orifices 484,486 and then out the ejection orifices 480,482. Because of the position of the ejection orifices 480,482, the ejection orifices 480,482 are well suited for controlling the characteristics of the gas exiting the gas chamber 454. Thus, the mass flow rate and flow characteristics of gas exiting the gas chamber 454 can be controlled by the outwardly positioned ejection orifices 480,482.

While the implementation of the ejection orifices 480,482 and retention orifices 484,486 provides a high degree of control of gas exiting the gas chamber 454, the retention orifices 484,486 may simply be a single section of the uniform cross-sectional area of the ejection orifices 480,482. The use and variations of the retention orifices 484, 486 will be discussed later, including adjustment of the relative positions.

The orifices 470,472 may be positioned within an inlet port 462 to eject gas from the gas chamber 454 into a first volume 440 and a second volume 442. This type of attachment allows for the gas exiting the gas chamber 454 to directly enter the first and

second volumes 440,442. Hence, a gas guide or other type of conduit used to channel the inflation gas from the inflator 424 to the inflatable curtain 410 is not required. The inflator 424 may simply be clamped in gas-tight fashion within the first and second inlet ports 460, 462, for example, through the use of ring-shaped clamps 464 that tightly press the fabric of the inlet ports 462 against the surface of the inflator 424.

The dual flow inflator 424 may be activated in a variety of ways to inflate the inflatable curtain 410. According to one embodiment, an initiator 4100 may initiate production of a high pressure stream of gas ejecting from the inflator 424. The type of initiator 4100 will depend upon the type of gas generant disposed in the inflators 424. For example, the gas generant may be a compressed gas, a liquid, or a solid that may be converted into a high pressure gas. Once the initiator 4100 begins converting the gas generant into high pressure gas, the gas is forced out of the inflator 424. The ejection of the inflation gas from the inflator 424 is obtained by the relatively high pressure gas within the inflator 424 moving to the relatively low pressure ambient environment.

By controlling the flow dynamics and physical properties of the gas exiting the inflator 424, the present inflator 424 provides highly controllable gas ejecting attributes.

This controllability provides the present inflator 424 with the ability to provide two selective and distinctive flows of gas into an inflatable curtain 410. In general, controlling the flow of gas exiting the inflator 424 is accomplished by controlling the mass flow rate of the exiting gas. Reviewing the variables that define the mass flow rate of a gas ejecting through an orifice provides an understanding of what characteristics of the inflator 424 may be varied to provide the desired control. The variables controlling the mass flow rate of a gas ejecting from an inflator 424 are established in the following equation: m = pVA wherein: m = mass flow rate of the fluid / ? = density of the fluid V velocity of the fluid A cross-sectional area of orifice The equation identifies three variables that control the mass flow rate of a gas: the orifice size, the velocity of fluid, and the fluid density. Because the gas is exiting the inflator 424 in a turbulent gas environment, the equation may not be completely linear.

This is a result of variations in the fluid density and rapid changes in the fluid velocity.

Furthermore, a compressible gas may also introduce inaccuracy into the equation.

However, a highly compressed gas, such as is present in an inflator 424, will function in a manner similar to a liquid for the purposes of mass flow rate characterization.

While the equation provided above does not provide a completely accurate calculation of the mass flow rate exiting the inflator 424, it does illustrate how each of the variables affects the mass flow rate. As illustrated in the equation above, one manner of controlling the mass flow rate of a gas exiting the inflator 424 is to control the effective cross-sectional area of the orifice 470,472 from which the gas is exiting. By maintaining the other variables at a generally constant value, the mass flow rate will increase or decrease in relation to the cross-sectional area of the orifice 470,472. As the cross- sectional area of the orifice 470,472 increases, the mass flow rate out of the orifice 470, 472 will correspondingly increase. Conversely, as the cross-sectional area of the orifice 470,472 decreases, the mass flow rate out of the orifice 470,472 decreases.

Figure 7 illustrates a dual flow inflator 424 where the first ejection orifice 480 of the first end 466 and the second ejection orifice 482 of the second end 468 are different sizes. The inflator 424 has a first ejection orifice 480 that has a larger effective cross- sectional area than the second ejection orifice 482. The difference in the effective cross- sectional areas of the orifices 480,482 is illustrated by the difference in the openings at the ends 466,468 of the inflator 424. The effective cross-sectional area of an orifice 480,482 may be defined as the area of the orifice 480,482 that operates to allow ejection of gas.

In Figure 7, the ejection orifices 480,482 are both illustrated as cross-sectional views of circular openings in the inflator 424. Thus, the diameters of circular openings are depicted. Because the area of an opening is a function of its diameter, the first ejection orifice 480 will have a larger cross-sectional area than the second ejection orifice 482.

The inflator 424, having two differently sized orifices 480,482 operates as the high pressure gas within the gas chamber 454 is produced. The high pressure gas is produced during an initiation sequence begun by the initiator 4100. The initiator 4100 causes the gas generant within the gas chamber 454 to be in a state where the gas may escape the inflator 424. This may entail converting the gas generant from a solid to a liquid, or entail opening sealing mechanisms in the gas chamber 454.

In one implementation, the sealing mechanism may be a plurality of burst disks 78 position within the retention orifices 484,486. The burst disks 478 may be generally

small and thin plates that block gas or the gas generant from escaping from the inflator 424. The burst disks 478 opens the inflator 424 when the initiator 4100 initiates. When the initiator 4100 initiates, the shockwave of the initiator 4100 discharging or the pressure of the gas created by the initiator 4100, forces the burst disks 478 through the retention orifices 484,486. The burst disks 478 are forced through the retention orifices 484,486 by the pressure or shock wave causing the burst disks 478 to deflect. Once the orifices 470,472 are open and the burst disks 478 are completely ejected through the orifices 470, 472, the burst disks 478 are captured by a screen 465.

Once the two ejection orifices 480,482 are open, the high pressure gas within the gas chamber 454 will move to the relatively low pressure ambient environment through the ejection orifices 480,482. In order for the gas to exit the inflator 424, the gas must pass through both orifices 470,472. As described above, the first orifice 470 and the second orifice 472 may have two or more separate sections; an ejection orifice 480,482, and a retention orifice 484,486.

In the inflator 424 illustrated in Figure 7, the ejection orifices 480,482 have a smaller effective cross-sectional area than the retention orifices 484,486. Because the most restrictive orifice through which a gas must pass will be the controlling orifice, the ejection orifices 480,482 will control the mass flow rate in the inflator 424 illustrated.

Thus, the effective cross-sectional areas of the ejection orifices 480,482 will establish the individual mass flow rates.

By allowing the ejection orifices 480,482 to control the mass flow rate of gas exiting the inflator 424, the first and second ejection orifices 480,482 may be individually adjusted and sized to provide individual mass flow rates. As illustrated in Figure 7 the first ejection orifice 480 is larger than the second ejection orifice 482. The varying sized inflator ejection orifices 480,482 may be independently adjusted to establish two distinct mass flow rates ejecting from the inflator 424. Each of the ejection orifices 480,482 will be sized to produce a selective mass flow rate.

For example, if a generally large mass flow rate is needed, a larger effective cross- sectional area will be established to create the desired flow rate. Alternatively, if a generally small mass flow rate is needed, then a smaller effective cross-sectional area will be established. The actual size of the cross-sectional area of the orifices 480,482 may be established through computation or through experimentation. Furthermore, the mass flow

rate required for each of the orifices 480,482 may be determined by size or the volumes 440 of the curtains 410 that are being inflated.

The effective cross-sectional area of the ejection orifices 480,482 can be controlled in many ways to establish the desired mass flow rate of gases exiting the inflator 424. The orifice 480,482 may have any number of shapes to control the mass flow rate of gas exiting an inflator 424. Generally, any shape can be used to control the mass flow rate out of the inflator 424 by selecting a desired cross-sectional area of the ejection orifice 480,482. Shapes such as rectangles, ovals, triangles, or various other shapes can be implemented to control the mass flow rates of gas ejecting out of an inflator 424. However, manufacturing concerns must be considered in selecting the orifice shape.

Because of these concerns, circular shaped orifices may often be preferred.

The ejection orifices 80,82 or other orifices 70,72 are generally adjusted to the desired effective cross-sectional area during the manufacturing process. Thus, the independently adjusted orifices 70,72, 80,82, 84,86 are adjusted during the manufacturing process based on previously determined mass flow rates. However, some variations of the present inflator 424 may include orifices 470,472, 480,482, 484,486 that are capable of being adjusted after the inflator is manufactured. This may be accomplished through the use of orifice inserts, protrusions, venting holes, or any other method of selectively controlling an effective cross-sectional area of an orifice 470,472, 480,482, 484,486 Referring now to Figure 8, the mass flow rate of gas ejecting from the inflator 424 may also be controlled at other locations along the inflator 424, besides at the ejection orifices 480,482. The first retention orifice 484 and the second retention orifice 486 may also be used to establish the mass flow rate. The dual flow inflator 424 illustrated in Figure 8 has a first retention orifice 484 and a second retention orifice 486 that are part of a system that seals the inflator 424. As discussed previously, the inflator 244 has an open state and a sealed state. Figure 8 depicts the inflator 424 in the sealed state. In one application, the sealed state may be maintained through a number of burst disks 478 obstructing gas from exiting through the retention orifices 484,486.

During initiation, the burst disks 478 or other sealing mechanisms are destroyed or forced away from their sealing positions. Once the inflator 424 is in the open state, gas may eject from the retention orifices 484,486. Generally, the retention orifices 484,486 are created to maintain the sealing mechanisms. In this capacity, it may be desirable for

the first retention orifice 484 and the second retention orifice 486 to be similarly sized.

For example, to simultaneously open two burst disks 478, it may be preferred for each burst disk 478 to span over a similarly sized retention orifice 484,486, allowing for symmetry in opening characteristics of the two ends 466,468.

However, as illustrated in Figure 8, the retention orifices 484,486 may be independently adjusted and sized to control the mass flow rate of gas exiting the inflator 424. For example, Figure 8 illustrates the first retention orifice 484 as being larger than the second retention orifice 486. Thus, the first retention orifice 484 will provide a larger mass flow rate than the second retention orifice 486. The mass flow rate of gas ejecting from the first retention orifice 484 and the second retention orifice 486 may be controlled in the same manner as the first and second ejection orifices 480,482.

However, because of the retention functions and the position of the retention orifices 484, 486 certain design considerations must be made to ensure proper function of the inflator 424. For example, gas exiting the first retention orifice 484 must subsequently pass through the first ejection orifice 480. Therefore, the size of the first ejection orifice 480 must be designed so as not to affect the mass flow rate of gas exiting the first retention orifice 484. Otherwise, if the first ejection orifice 480 has a smaller effective cross- sectional area than the first retention orifice 484, then the cross-sectional area of the first ejection orifice 480 will control the overall mass flow rate. To avoid having conflicting mass flow rate mechanisms, the ejection orifices 480,482 should generally have a larger effective cross-sectional area than the retention orifices 484,486. If the ejection orifices 480,482 are larger than the retention orifices 484,486, then the mass flow rate will be controlled by the smaller retention orifices 484,486.

Alternatively, the ejection orifices 480,482 and the retention orifices 484,486 may comprise a single orifice 470,472 having a single effective cross-sectional area. Such an orifice 470,472 design would operate similarly to the orifices 480,482, 484,486 described above. However, no distinction would be made between the ejection orifices 480,482 and the retention orifices 484,486.

Another consideration when adjusting the mass flow rate through use of the retention orifices 484,486 is the operation of the burst disks 478. The burst disks 478 are designed to be forced through the retention orifices 484,486 at a determined pressure or in response to a predetermined shock wave. As the size of the retention orifices 484,486 change, the design of the burst disks 478 must also be changed to maintain a selective

opening time, if so desired. This may require that the structure of the burst disks 478 be modified to maintain a desired opening time. A weaker burst disk 478 would span over a smaller retention orifice 484,486, such as the second retention orifice 486, and a comparatively stronger burst disk 478 would span over the larger retention orifice 484.

Such calculations could be made with common fixed-fixed beam or thin plate deflection equations.

Beyond the use of selectively sized orifices 470,472, 480,482, 484,486 to control the mass flow rate of gas exiting the inflator 424, other mechanisms may be employed.

Figures 9A, 9B and Figures 10A, 10B illustrate another mechanism for controlling the mass flow rate of gas exiting an inflator 424.

Referring now to Figures 9A & 9B, two ejection orifices 4210,4220 are illustrated having two different effective cross-sectional areas 4214, 4224 controlled through varying sized obstructions 4218,4228 placed in the orifices 4210,4220. As can be seen in Figure 9A, the first obstruction 4218 is smaller than the second obstruction 4228 in Figure 9B, while the overall diameter of the orifices 4210,4220 are similar. The smaller obstruction 4218 allows a larger effective cross-sectional area 4214 for the first orifice 4210, i. e. a larger area for gas to pass through. Conversely, the second orifice 4220, having the larger obstruction 4228, will have a lower mass flow rate.

The obstructions 4218,4228 would not require different orifice 4210,4220 diameters between the first end 466 and the second end 468 of an inflator 424 to control the mass flow rates. Rather, a single orifice 4210,4220 diameter may be used at both ends of the inflator 424. Then, the differing sized obstructions 4218,4228 may be placed in the path of the ejecting gas to limit the mass flow rates without changing the diameters of the orifices 4210,4220. The different sized obstructions 4218,4228 in opposing ends will function similarly to different sized orifices 470,472.

Figures 9A & 9B illustrates the obstructions 4218,4228 as being circular shaped sections generally located within the center of the orifices 4210,4220. However, other shapes and types of obstructions are also possible. Figures 10A & 10B illustrates an alternative embodiment of an obstruction 4238,4248 positioned within an orifice 4230, 4240. The obstructions 4238,4248 illustrated in Figures 10A & 10B differ from the obstructions 4218,4228 illustrated in Figures 9A & 9B by their shape and potential modular nature. The obstructions 4238,4248 of Figures 10A & 10B are pins rather than

circular shaped members. The obstruction pins 4238,4248 would similarly limit the effective cross-sectional areas 4234,4244 of the two orifices 4230,4240.

The pin obstructions 4238,4248 may have some advantages over the circular shaped obstructions for manufacturing purposes. The pin obstructions 4238,4248 may be added to the orifices 4230,4240 simply by placing the pins 4238,4248 through holes located adjacent to the orifice is 4230,4240. This would allow the mass flow rates of the two orifices 4230,4240 to be independently adjusted after the inflator 424 body is manufactured. However, variations of the obstructions 4218,4228 illustrated in Figure 9A & 9B may also provide for varying the effective cross-sectional areas 4214,4224 in a post manufacturing situation.

Another variation that may be applied to the obstruction embodiment is to make the obstructions 4218,4228, 4238,4248 adjustable. For example, the pin obstructions 4238,4248 may be a threaded mechanism that can be selectively adjusted into an out of the orifices 4230,4240. Thus, only a portion of the pin obstruction 4238,4248 would extend into the orifice 4230,4240. Furthermore, other designs and mechanisms of adjusting the circular obstructions 4218,4228 illustrated in Figure 9A & B may be employed to adjust the size of the obstructions 4218,4228.

Referring now to Figure 11, another mechanism for controlling the mass flow rate of an inflator 424 is illustrated. The inflator 424 may be configured with a venting hole or bleed line 4310 for ejecting an amount of gas out of the inflator 424 but not into the inflatable curtain. A bleed line 4310 is simply an additional orifice from which gas may be ejected. However the gas would not be ejected into the inflatable curtain 410. Instead, the gas would be vented to another location at a point before the ejection orifices 480,482.

Because the bleed line 4310 would divert a mass flow of gas away from the inflatable curtain 410, the diverted mass of gas would be subtracted from the mass flow of gas originally ejected toward the specific inflator end 466,468. Thus, a bleed line 4310 placed at the first end 466 of the inflator 424 would cause the mass flow rate of gas ejecting from the first end 466 to be less than the mass flow rate of gas ejecting from the second end 468. The effect would be similar to having two different orifice sizes 470,472 on each of the ends 466,468.

The size-of the bleed line 4310 could be sized, similar to the ejection orifices 480, 482, to eject a controlled amount of gas out of the inflator 424. The amount of gas could be precisely calculated to provide varying mass flow rates out of each of the ends 466,468

of the inflator 424. Furthermore, a bleed line 4310 may be located in one or more of the ends 466,468 of the inflator 424. Where each bleed line 4310 ejects a controlled amount of gas. Additionally, more than one bleed line 4310 may be present in each end 466,468 of the inflator 424.

A further mechanism for controlling the mass flow rate of a gas exiting an inflator 424 is an inflator module 4410 comprised of a first inflator 4416 and a second inflator 4420 as illustrated in Figure 12. The first inflator 4416 and the second inflator 4420 may be connected at their bases 4424,4428 by a coupling member 4432. The coupling member 4432 maintains the relative position of the two inflators 4416,4420, such that gas ejecting from the first inflator 4416 and gas ejecting from the second inflator 4420 eject in substantially opposite directions.

In the module 4410 illustrated in Figure 12, the first inflator 4416 and the second inflator 4420 may be configured to eject gas at two different mass flow rates. In one implementation, the two inflators 4416,4420 may have differently sized orifices 4436, 4440, as illustrated in Figure 12. This configuration would function similarly to the inflator 424 illustrated in Figure 7. This is represented by the difference in the cross- sectional areas of the openings at the two orifices 4436,4440. By coupling the two inflators 4416,4420 together, the two inflators 4416,4420 may operate as a single inflator 424 having two differently sized orifices 4436,4440 for ejecting a gas.

In the inflator module 4410 of Figure 12, both of the inflators 4416,4420 have an individual initiator 4444,4448 to induce an open configuration. The initiators 4444,4448 can be configured to simultaneously initiate both inflators 4416,4420 or may alternatively initiate the inflators 4416,4420 at different times. Variations of the inflator module 4410 may have the two inflators 4416,4420 sharing a common initiator. This would reduce the part count and thus reduce the cost of the inflator module 4410. However, this may also increase the manufacturing cost associated with inserting a single initiator into two inflators 4416,4420.

Another implementation of the inflator module 4410 illustrated in Figure 12, involves the use of different gas generants or gas generant quantities in each of the inflators 4416,4420. The first inflator 4416 is illustrated as having a higher density of gas generant 4452 than the second inflator 4420. In context of the equation previously cited, this would be equivalent to changing the density of the gas within a single inflator 424.

Thus, a different mass flow rate could be achieved through two inflators 4416,4420 each having a similarly sized ejection orifice 4436,4440.

For example, the first inflator 4416 could eject a higher mass flow rate of gas than could the second inflator 4420. This could be caused because by the higher density of gas generant 4452 in the first inflator 4416 compared to the gas generant 4456 in the second inflator 4420. Alternatively, the use of different gas generant densities 4452,4456 could be combined with differing sized ejection orifices 4436,4440. Such a configuration could provide for a large range of controllability of two separate mass flow rates of gas out of the inflator module 4410.

Other similar types of inflator designs may simply divide an inflator into two different chambers, where each of the chambers is configured to eject a different mass flow rate of gas. The chambers could incorporate varying amounts and different types of gases to control the mass flow rate. The inflator may also be any number of shapes. The inflators previously illustrated have been generally elongated. However, the inflators can be any shape that allows for two individually adjustable mass flow rates to eject from the inflator and into an inflatable curtain.

Because the inflators previously discussed provide different mass flow rates of gas between the two opposing ends, the inflator is not completely thrust neutral. For example,. in the inflator 424 of Figure 7 the first ejection orifice 480 is larger than the second ejection orifice 482. The difference in the sizes of the orifices 480,482 produces two different mass flow rates which in turn produce two different thrusts. Because the mass flow rate of gas ejecting from the first ejection orifice 480 is larger than the mass flow rate of gas ejecting from the second orifice 482, the inflator 424 will have a positive thrust in a negative longitudinal direction 413.

However, because the thrust from the first orifice 480 and the thrust from the second orifice 482 are in substantially opposite directions, they may substantially cancel each other out. For example, a thrust from the first orifice 480 will be in a negative longitudinal direction 413 and a thrust from the second orifice 482 will be in a positive longitudinal direction 413. These substantially opposite thrust directions will tend to cancel each other out, to the extent that they are equal. Thus, the thrust of the inflator 424 will be equal to the thrust produced by the first orifice 480 subtracted by the thrust produced by the second orifice 482.

While the thrust may be substantially reduced, it may be desired in some instances for the inflator 424 to be entirety thrust neutral in a single direction. Figure 13 illustrates an inflator 4510 capable of being thrust neutral along a single axis. The thrust neutral configuration is maintained in a single direction at the expense of thrust into an opposite direction, as will be illustrated below.

Referring now to Figure 13, the inflator 4510 has a first end 4512 and a second end 4514. The first end 4512 and the second end 4514 are configured to eject a flow of gas out of the first orifice 4514 and the second orifice 4517 respectively. In the inflator 4510 illustrated, the first orifice 4516 is larger than the second orifice 4517, such that the first orifice 4514 ejects gas at a higher mass flow rate than the second orifice 4517. Thus, the larger mass flow rate of gas ejecting from the first orifice 4516 will produce a larger thrust at the first end 4512 than the thrust produced by the second orifice 4517 at the second end 4514.

To compensate for the thrust differential, the first end 4512 has an angled section 4518, where the first end 4512 and the second and 4514 do not share a common axis 4519.

The angled section 4518 of the first end 4512 produces a thrust 4520 that is not in the same axis 4519 as a thrust 4524 produced at the second end 4514. The gas ejected from the first end 4512 produces a first thrust 4520, where the first thrust 4520 has a longitudinal component 4521 and a transverse component 4522. The gas ejected from the second end 4514 produces a thrust 4524 with only a longitudinal component 4525.

The angled section 4518 will establish the longitudinal component 4522 and the transverse component 4521 of the first thrust 4520. By selectively controlling the angle of the angled section 4518, the longitudinal component 4522 of the first thrust 4520 can be made equal to the entire longitudinal component 4525 of the second thrust 4524. Because the longitudinal component 4522 of the first thrust 4520 is in a substantially opposite direction than the longitudinal component 4525 of the second thrust 4524, the inflator 4510 will be thrust neutral along the axis 4519.

While the inflator 4510 will not be thrust neutral in the lateral direction 414, the shape and mounting of the inflator 4510 generally may make the lateral 414 thrust of little consequence. For example, some attachment mechanisms that attach the inflator 4510 to the structure of the automobile 412 may be susceptible to disengaging the inflator 4510 in the presence of a net longitudinal 413 thrust. However, the implementation of an angled section 4518 in the inflator 4510 can eliminate substantially all thrust in the longitudinal

direction 413. Thus, only a transverse component 4521 of the first thrust 4520 will remain. Because the biaxial flow inflator 4510 is generally mounted along the roof rail of an automobile 412, the transverse thrust component 4521 will force the inflator 4510 against the automobile's 412 structure. Such an inflator 4510 implementing an angled section 4518 may have various applications in controlling the gas flow and thrust of gas ejecting from the inflator 4510.

Referring now to Figure 14, an alternative embodiment of the inflator 424 is illustrated where the flow rate of gas ejecting from the inflator 424 is controlled by choking orifices 493a, 493b. In the inflator 424 illustrated, the retention orifices 484,486 are substantially the same size to emit an equal mass flow rate from each orifice 484,486.

The retention orifices 484,486 may provide a channel having a generally uniform cross- section from the interior of the inflator 424.

In this embodiment, the flow rate of gas exiting the inflator 424 is controlled by the choking orifices 493a, 493b positioned laterally 414 outward from the retention orifices 484,486. As illustrated, the first choking orifice 493a may have a smaller opening than the second choking orifice 493b. Thus, the flow rate of gas ejecting from the inflator may be controlled by the choking orifices 493a, 493b, such that the gas ejecting from the first choking orifice 493a has a smaller mass flow rate than the gas ejecting from the second choking orifice 493b.

As was previously noted, in order for the choking orifices 493a, 493b to control the mass flow rate of gas ejecting from the inflator 424, the retention orifices 484,486 must be larger than the choking orifices 493a, 493b. Furthermore, the choking orifices 493a, 493b need not necessarily be a necked-down section in the end 492 of the inflator 424.

The choking orifices 493a, 493b may be crimped ends of the inflator where the gas exiting the choking orifices 493a, 493b directly enters the airbag.

Implementing inflators having independently adjustable mass flow rates allows a single inflator design to be applied to a large number of inflatable curtain designs and configurations. Furthermore, the independently adjustable orifices provide a large range of control for the deployment characteristics of singular or multiple inflatable curtains.

Referring now to Figure 15, an inflatable curtain 4620 coupled to a biaxial inflator 4624 is illustrated. The inflatable curtain 4620 has a first volume 4632 and a second volume 4636 that are not equally sized, where the first volume 4632 is larger than the second volume 4636.

In order to simultaneously and instantaneously fill both inflatable curtain volumes 4632,4636, the mass flow rate of gas ejecting from the first end 4640 of the inflator 4624 should be larger than the mass flow rate of gas ejecting from the second end 4644. The difference in mass flow rates can be selected according to the different sizes of inflatable curtain volumes 4632,4636. This may be accomplished through any of the above discussed mechanisms, such as an inflator 4624 having two differently sized ejection orifices. Thus, the size of the orifices could be sized to the inflatable curtain 4620 volumes 4632,4636.

The independently adjustable inflator 4624 can be implemented in different inflatable curtain 4620 configurations. For example, the first volume 4632 and second volume 4636 of the inflatable curtain 4620 may be configured such that gas cannot flow between the two volumes 4632,4636. In other embodiments, the first volume 4632 and the second volume 4636 may be in fluid communication, allowing gas to flow from one volume 4632 to the other 4636. By adjusting the mass flow rate for either design, the inflation characteristics of the inflatable curtain 4620 may be controlled.

Other inflatable curtain 4620 designs may not have two separate volumes 4632, 4636, but rather would have a single rectangular shaped volume fed by both ends of the inflator 4624. The independently adjustable inflator 4624 could be used when the inflator 4624 is not in the center of the rectangular shaped inflatable curtain 4620. The mass flow rates could be designed to eject an amount of gas that corresponds to the size of the sections of the inflatable curtain 4620 that the inflator 4624 must fill. While an inflator 4624 with a non-adjusted mass flow rate could still fill a large rectangular shaped inflatable curtain 4620, the adjustable mass flow rates allow for both sections to be inflated simultaneously, even if differences in the size of the sections is large.

Another application of the independently adjustable mass flow rates is the ability to control deployment sequences of multiple inflatable curtains 4620 or multiple sections of a single curtain 4620. For example, the inflatable curtain 4620 of Figure 15 has two separate volumes 4632,4636. In some deployment conditions it may be desirable for one of the volumes 4632 to be inflated before the other 4636. By varying the mass flow rates of the gas ejecting into each volume 4632,4636, the first volume 4632 can be made to inflate before the second volume 4636. The mass flow rates of the ends 4640,4644 of the inflator 4624 can be used with any number of differently sized volumes 4632,4636.

Furthermore, the inflator 4624 can also inflate one side of a single inflatable curtain 4620 before the other, or have a larger instantaneous pressure than the other side.

The inflator described above can have a number of embodiments by varying the shape, orientation, sequence, positioning, or other variables of the inflator. The inflator can be broadly described as an inflator configured to eject a gas at a first mass flow rate from a first orifice and eject a gas at a second mass flow rate from a second orifice. By varying the mass flow rates the inflator can controllably inflate a wide range of inflatable curtain designs.

Referring to Figure 16, an inflatable curtain 710 according to one embodiment of the invention is shown installed in a vehicle 712. The inflatable curtain 710 may form part of an airbag system configured to protect one or more vehicle occupants against lateral impact through the formation of a protective curtain beside the occupants.

The vehicle 712 has a longitudinal direction 713, a lateral direction 714, and a transverse direction 715. The vehicle 712 further has front seats 716 laterally displaced from first lateral surfaces 717, or front doors 717, as shown in the vehicle 712 of Figure 16. The vehicle 712 also has rear seats 718 laterally displaced from second lateral surfaces 719, or rear doors 719, as depicted. As shown, two such inflatable curtains 710 may be used: one for the driver's side of the vehicle 712, and the other for the passenger's side.

One or more accelerometers 711 or other similar impact sensing devices are used to detect sudden lateral acceleration (or deceleration) of the vehicle 712 and transmit electric signals via electric lines 731 to one or more inflators 720 that provide flows of pressurized gas to inflate the inflatable curtains 710. As shown in Figure 16, a single inflator 720 may be used to inflate each of the inflatable curtains 710. Specifically, a single inflator 720 may be used to inflate the first protection zone 740 and the second protection zone 742 of each inflatable curtain 710. The inflator 720 may be affixed to the vehicle 712 through the use of relatively simple mounting brackets 729.

The inflators 720 may be positioned approximately midway along the longitudinal length of the inflatable curtains 710 to provide relatively rapid and even inflation of the first and second protection zones 740,742 in a manner that will be described in greater detail subsequently. Each of the inflators 720 may take the form of a hollow pressure vessel containing a chemically reactive material and/or compressed gas referred to as an "inflation charge"that can be activated or released upon initiation of the inflator 720 to

provide an outflow of inflation gases. In the embodiment of Figure 16, the inflators 720 are partially enveloped within the inflatable curtains 710 so that inflation gases exiting the inflators 720 flow directly into the inflatable curtains 710. The inflators 720 may operate with such rapidity that, before the vehicle 712 has fully reacted to the impact, the inflatable curtains 710 have inflated to protect vehicle occupants from impact.

Additionally, the inflators 720 may operate in such a prolonged manner that the inflatable curtains may remain inflated or be reinflated throughout the impact event or vehicle rollover.

Optionally, the accelerometer 711 may be stowed within an engine compartment 730 or dashboard 732 of the vehicle 712. A controller (not shown) may also be used to process the output from the accelerometer 711 and control various other aspects of a vehicle safety system of the vehicle 712. Such a controller may also, for example, be positioned in the engine compartment 730 or dashboard 732, proximate the accelerometer 711. Such a controller could be configured to sequentially fire the initiators in a"smart airbag"when a rollover event or other event requiring extended inflation was detected. In such configurations, the electric line 731 and/or other control wiring may be disposed along the A pillars 734 of the vehicle 712, located on either side of the windshield 735, to reach the inflators 720. Alternatively, each accelerometer 711 may be positioned near one of the inflators 720, as shown in Figure 16.

The inflators 720 and the inflatable curtains 710 may be installed by attaching them to roof rails 736 of the vehicle 712. Depending on the model of the vehicle 712 and the desired configuration of the inflatable curtains 710, airbag components may also be disposed along the B pillars 737, C pillars 738, and/or D pillars 739.

The inflatable curtains 710 shown in Figure 16 are configured to protect not only occupants of the front seats 716, but those of the rear seats 718 as well. Thus, each inflatable curtain 710 may have a first protection zone 740 configured to inflate between a front seat 16 and one of the front doors 717, and a second protection zone 742 configured to inflate between a rear seat 718 and a rear door 719. The first and second protection zones 740,742 may be adapted to be separate individual cushions that are isolated from each other. However, the inflatable curtains 710 may optionally be parts of the same cushion, i. e. , the first and second protection zones 740,742 may be in fluid communication with each other. This could be true even when inflation gas is able to flow through the inflator 720 between the first and second protection zones 740,742, or if there

is no flow allowed through the inflator. The first and second protection zones 740,742 of each inflatable curtain 710 may be attached together through the use of a connection zone 744 positioned between the protection zones 740,742. The connection zone 744 may provide a flow path through which gases can flow between the first and second protection zones 740,742.

Each of the inflatable curtains 710 may have a front tether 746 attached to the A pillar 734 and a rear tether 748 attached to the roof rail 736 to exert tension on the inflatable curtains 710 to keep them in place during inflation and impact. Those of skill in the art will recognize that the tethers 746,748 may also be attached to other parts of the vehicle 712, such as the B pillars 737, C pillars 738, and/or D pillars 739. The tethers 746, 748 may be constructed of standard seatbelt webbing or the like.

Although each inflatable curtain 710 in Figure 16 has two protection zones 740, 742, the invention encompasses the use of inflatable curtains with any number of protection zones. Thus, if desired, each of the inflatable curtains 710 may be extended to have one or more protection zones positioned to protect occupants of extra seats 750 behind the rear seats 718 from impact against third lateral surfaces 752 of the vehicle 712.

Additional inflators 720 may be used to inflate such additional protection zones.

The inflators 720 of the invention may be uniquely configured to provide rapid, even inflation as well as simple and inexpensive manufacturing and installation. Figure 16 further shows a slightly enlarged perspective view of an inflator 720 including primary gas chamber 766, secondary gas chamber 768, and flow restrictor 780. The inflator also comprises initiation assembly 7100, attached to the accelerometer 711 of the vehicle 712 by electric line 731. The inflator 720 is attached to the first and second inlet ports 760, 762, of the inflatable curtain 710 by clamps 764. Additionally, the inflator 720 is attached to the vehicle 712 by mounting brackets 729. The configuration of the inflator 720 will be described in greater detail in connection with Figure 17.

Referring to Figure 17, a side elevation, cross sectional view of the inflator 720 is shown. The inflator 720 may have a primary gas chamber 766 formed of a material with a comparatively high tensile strength such as steel, for retaining the inflation charge. The primary gas chamber 766 may be formed of a single, unitary piece. In the alternative, the primary gas chamber 766 may be made from multiple pieces that are welded or otherwise attached together. The primary gas chamber 766 may have a generally tubular shape, but

may also be flattened, hemispherical, or otherwise shaped to accommodate the space available in a vehicle.

The primary gas chamber 766 may be positioned within the first and second inlet ports 760,762 of the protection zones 740,742 of inflatable curtain 710 so that inflation gas from the first and second primary flows of gas 794a, 794b leaving the primary gas chamber 766 directly enters the first and second protection zones 740,742. Hence, no gas guide or other type of conduit used to channel the inflation gas from the inflator 720 to the inflatable curtain 710 is required. The inflator 720 may simply be clamped in gas-tight fashion within the first inlet port 760, for example, through the use of ring-shaped clamps 764 that tightly press the fabric of the inlet port 760 against the outer surface of the inflator 720.

The dimensions of the primary gas chamber 766 may be varied to suit the volume in which the primary gas chamber 766 is to be installed. For example, the primary gas chamber 766 may be made longer in the longitudinal direction 713 and/or thinner in the lateral and transverse directions 714,715 to facilitate installation in a long, narrow space such as the space beside the roof rail 736. A longer primary gas chamber 766 may be installed such that the primary gas chamber 766 extends a significant distance into each protection zone 740,742. Such installation may advantageously provide inflation gas flows that enter the inflatable curtain 710 about midway through the protection zones 740, 742 for more even inflation.

The primary gas chamber 766 may have a first exit orifice 770 disposed within the first inlet port 760 of the airbag and a second exit orifice 772 disposed within the second inlet port 762 of the airbag. The exit orifices 770,772 have an open configuration, in which inflation gas can pass relatively freely through them, and a sealed configuration, in which substantially all inflation gasses are trapped within the primary gas chamber 766.

Consequently, herein"exit orifice"refers to a passageway as well as to the structure that provides selective closure of the passageway.

More precisely, the exit orifices 770,772 include an interior cap 774a, as illustrated in Figure 17. This interior cap 774a, 774b may have an opening 776a, 776b against which a burst disc 778a, 778b is pressed by the pressure within the gas chamber 766. A third burst disc, 778c, may be placed over the initiator aperture 7102, and be held in place, at least in part, against the initiator assembly 7100, by the pressure within the chamber 766. The burst discs 778a, 778b, 778c may have a wide variety of configurations.

Specifically, if desired, each of the burst discs 778a, 778b, 778c may have a slightly domed shape to provide a tight seal with the circular shape of the associated opening 776a, 776b, 7102.

The burst discs 778a, 778b, 778c are preferably shaped to deflect under a pressure shock and/or increase to uncover the openings 776a, 776b, 7102. For example, the burst discs 778a, 778b may be made to bend enough to fit through the openings 776a, 776b, so that a pressure shock and/or increase ejects the burst discs 778a, 778b from the openings 776a, 776b. The burst discs 778a, 778b may simply have a pressure threshold above which sufficient deformation occurs to push the burst discs 778a, 778b through the openings 776a, 776b. Alternatively, the burst discs 778a, 778b, 778c may deform primarily in response to shock, or rapid pressure changes within the gas chamber 766.

In order to prevent the ejected burst discs from damaging the inflatable curtain 710, the inflator 720 may also have a pair of burst disc retention members 790a, 790b, each of which is disposed outside one of the exit orifices 770,772. The burst disc retention members 790a, 790b may have a wide variety of configurations. As illustrated, the burst disc retention members 790a, 790b may take the form of thickened pads or screens through which inflation gases pass relatively freely. The burst discs 778a, 778b, 778c are captured by the burst disc retention members 790a, 790b after ejection from the openings 776a, 776b. The burst discs 778a, 778b, 778c may remain in front of the openings 776a, 776b, in which case inflation gases must simply flow around the burst discs 778a, 778b, 778c to exit the inflator 720.

The inflator 720 may also have ejection nozzles 792a, 792b disposed outside the first and second exit orifices 770,772 and the burst disc retention members 790a, 790b.

These ejection nozzles 792a, 792b may assist in modifying the amount and/or speed of the primary and secondary flows of gas that issue from the inflator. In many inflators of the invention, the ejection nozzles 792a, 792b are tuned equally to provide an equal thrust and amount of gas flow through each nozzle. Such a configuration yields an inflator with no net thrust along the longitudinal axis of the inflator.

Inflators according to the invention may alternatively be made in a non-thrust- neutral manner. For example, the first and second exit orifices 770,772, or the ejection nozzles 792a, 792b need not be equal in size, but may be sized differently to provide varying amounts of inflation gas out of each exit orifice. Such unequal flows may be desirable in circumstances where the first and second protection zones 740,742 are sized

differently. In such a circumstance, the thrust from one of the gas flows 794a, 794b or 796a, 796b may only partially negate the thrust of the other gas flow 794a, 794b, or 796a, 796b. Varying degrees of longitudinal support may be provided to account for such inequalities in thrust.

The dual-stage inflator 720 of this invention also includes a secondary gas chamber 768 and a flow restrictor 780. This secondary gas chamber 768 is configured to retain an inflation charge including a gas generant 784b, and to provide a secondary flow of gas 796 into the primary gas chamber 766. The secondary gas chamber 768 is configured to retain an inflation charge in a manner similar to the primary gas chamber 766. The inflation charge of the secondary gas chamber 768 may be the same as the inflation charge of the primary gas chamber 766, or alternatively, the inflation charge may be different in composition, pressure, or form.

The secondary gas chamber 768 is connected to the primary gas chamber 766 by a flow restrictor 780. This flow restrictor 780 may be shaped as a connecting ring with a flow restrictor orifice 782. The flow restrictor 780 may additionally comprise a frangible seal such as a burst disc, a scored surface, or a compression seam.

The secondary gas chamber 768 of this invention is configured to provide a secondary flow of gas 796 to an airbag coupled to the inflator 720 to initially inflate the airbag, and then to maintain that inflation for a period of time. The initial inflation may be largely provided by the inflation charge of the primary gas chamber 766 and the first and second primary flows of gas 794a, 794b it produces. The maintenance of the initial inflation may largely be provided by the secondary flow of gas 796 from the secondary gas chamber 768. The maintenance, or secondary flow of gas 796 may be delivered by providing a flow restrictor 780 that may take the form of a restricted flow channel 779.

Such a restricted flow channel 779 may be a capillary tube with a narrow flow restrictor orifice 782. This combination limits the rate at which the inflation charge housed in the secondary gas chamber 768 may escape. The flow channel 779 may be defined by a flow restrictor orifice radius 781 and a flow restrictor orifice diameter 783.

In inflators such as 720 that are configured such that the flow restrictor 780 has no component which completely closes the restrictor, the inflation charges of the primary and secondary gas chambers 766,768 may mingle freely. As a result of this, no pressure differential between the gas chambers 766,768 may be maintained.

The inflator 720 of the invention may alternatively provide the secondary flow of gas 796 by providing a frangible seal on the flow restrictor 780. Suitable frangible seals may include burst discs (such as burst discs 778a, 778b used with the primary gas chamber 766), scored surfaces (not shown), and compression seams (not shown). These seals may be placed to prevent gas flow from the secondary gas chamber 768 until the airbag has been activated.

Frangible seals such as those optionally used with the primary and secondary gas chambers 766,768 include surfaces that open when the pressure within the gas chambers 766,768 exceeds the strength of the surfaces.

One such frangible seal is a scored surface. Scored surfaces have scores that are weakened regions formed by gouging the surface. Such a score could, for example, be formed with a sharpened tool constructed of hard steel, tungsten carbide, diamond, or the like. The tool may be shaped to peel off a layer of the material of the surface, and multiple operations may be used to remove the desired amount of material. Such scores could take a wide variety of configurations. In one example, each score may simply comprise a single line disposed within the plane perpendicular to the transverse direction in relation to the surface. Alternatively, a star-like shape with multiple intersecting scores may be used.

With a star-like shape, multiple wedge-shaped deformable portions would exist between the intersecting scores, and each deformable portion would bend or"bloom"outward upon failure of the scores.

The depth of scores may be selected such that the score ruptures when the pressure within the gas chamber reaches a predetermined threshold, or when the pressure shock within the gas chamber reaches a predetermined threshold. A deeper score would produce an opening that opens in response to a lower pressure or shock. Additionally, scores could be made of an equal depth to ensure that the scored surfaces open simultaneously.

Further, individual scores may be varied in depth, length, width, or configuration to provide different timing and/or gas flow characteristics for the inflator.

Some score configurations produce a set of lips upon failure that may deflect outward somewhat to reach a deformed configuration. In the deformed configuration, the lips may be separated somewhat to provide an opening through which inflation gas can escape. In this configuration, the lips perform the functions accomplished by the openings and the ejection nozzles used alternatively. Indeed, the lips may be configured to deflect such that an opening of a desired size is produced.

A"compression closure"may be defined as an opening that has been closed, or nearly closed, through mechanical deformation of the material surrounding the opening.

Thus, compression closures include openings that have been crimped, swaged, twisted, folded, or otherwise deformed into a closed position. Such closures may be formed through methods including the application of mechanical compression perpendicular to the axis of the opening. This compression may form a crimp or weld which may rupture in response to a high pressure or pressure shock within the gas chamber the crimp or weld is sealing. This rupture would result in the seal taking on a deformed configuration that permits the inflation gas to escape the gas chamber. The compressive force applied to close the lips and the weld strength of the weld may be selected to obtain a desired threshold pressure or shock.

Where multiple frangible seals are used in an inflator such as an inflator with multiple compartments, features such as the size and depth of a score, and the compressive force and the weld strength of a compression seam may be toleranced somewhat tightly to ensure that the frangible seals open simultaneously.

The frangible seal surface may in some cases be placed outside of the exit orifice to open to form a suitable ejection nozzle (in the place of ejection nozzles 792a, 792b) for the secondary gas chamber 768 or the first and second exit orifices 770,772. Such configurations allow for different substances to be used for inflation charges in the primary and secondary gas chambers 766,768, and also allow for the use of inflation charges with different pressures in the gas chambers 766,768.

Frangible seals such as burst discs may preferably be used in inflators in which the inflation charge of a secondary gas chamber 768 at least partially comprises a liquid gas producing material 786 such as a liquefied gas. In such applications, the seals segregate the liquid 786 from the primary gas chamber 766. In those inflators 720 of the invention that have burst discs 778a, 778b, a burst disc retention member 790a, 790b may further be included to trap and retain a spent burst disc 778a, 778b and prevent its ejection from the inflator 720.

In inflators 720 of the invention that use a frangible seal over the flow restrictor orifice, the frangible seal may be made to rupture at a specific pressure differential between the primary and secondary gas chambers 766, 768. One example of this would be an inflator in which the secondary gas chamber contained a gas pressurized to 3,000 psi and the primary gas chamber contained a gas pressurized to 2,000 psi, in which the burst

disc between the gas chambers was constructed to burst at a pressure difference of 2,500 psi. After initiation of the inflator, as the primary flows of gas from the primary gas chamber begin, the pressure difference between the gas chambers increases. When the pressure of the primary gas chamber reaches about 500 psi, the burst disc would rupture.

This would open the flow restrictor orifice between the primary and secondary gas chambers, and the gas generant from the secondary gas chamber would produce a secondary flow of gas that would add to the primary flow of gas created during the initiation of the airbag. This secondary flow may be used to keep the airbag inflated for an extended period of time, or to reinflate the airbag.

According to the present invention, such dual-stage inflators may include additional primary and/or secondary chambers to extend the length of time for which the inflator is capable of providing a flow of gas, as well as to increase the amount of gas that the inflator is capable of producing. Such additional secondary chambers may be placed along a longitudinal axis shared by the other secondary and primary gas chambers, or they may be placed along other axes at angles to the other gas chambers.

Upon deployment of the inflator 720, a first primary gas flow 794a may exit the primary gas chamber 766 via the first exit orifice 770, and a second primary gas flow 794b may exit the primary gas chamber 766 via the second exit orifice 772. A secondary gas flow 796 may then exit the secondary gas chamber 768 via the flow restrictor orifice 782.

These gas flows may be smoothly integrated and indistinguishable from each other, or they may be separated by sufficient time that the primary and secondary gas flows are distinguishable. The primary and secondary gas flows 794a, 794b, and 796 may then travel to reach the corresponding inlet ports 760,762 of the inflatable curtain 710. As shown, the primary and secondary gas flows 794a, 794b, and 796 travel in the longitudinal direction 713, along the longitudinal axis 758 of the inflator 720.

The inflator 720 may be comparatively easily installed in the vehicle 712 to obtain the configuration depicted in Figure 16. For example, the first end 771 of the primary gas chamber 766 may be inserted into the first inlet port 760 of the curtain 710, and the second end of the primary gas chamber 773 may be inserted into the second inlet port 762 of the curtain 710. The inflatable curtain 710 may then be attached to the roof rail 736 in the position shown in Figure 16, and the inflator 720 may be attached to the roof rail 736 with mounting brackets such as mounting brackets 729.

The steps described above for installing the airbag inflator may be reordered in many ways to suit the particular configuration of the vehicle 712. For example, the inflator 720 may first be attached to the roof rail 736 with the mounting brackets 729, and the inlet ports 760,762 may then be fitted around the primary gas chamber 766. The inflatable cushion 710 may then be fixed in place.

The ejection nozzles 792a, 792b are optional; inflation gases may simply be allowed to freely escape the inflator 720. However, the ejection nozzles 792a, 792b may beneficially provide more accurate direction of the primary and secondary gas flows 794a, 794b, and 796. The ejection nozzles 792a, 792b may also increase the speed with which the primary and secondary gas flows 794a, 794b, and 796 escape the inflator 720, so that the gas flows have the momentum to travel further into the inflatable curtain 710. Such rapid ejection may help to ensure that the portions of the inflatable curtain 710 that are furthest from the inflator 720 are adequately inflated prior to impact of the vehicle occupant against the inflatable curtain 710.

A dual flow biaxial inflator may be activated in a variety of ways to inflate the inflatable curtain 710. In one inflator, the primary and secondary gas flows 794a, 794b, and 796 may both be triggered by the action of a single initiation assembly 7100. The initiation assembly 7100 may have an assembly aperture 7101 that is in communication with the interior of the primary gas chamber 766. The initiation assembly 7100 may, for example, be laser welded in place to prevent the escape of inflation gases through the initiator aperture 7102 or ejection of the initiation assembly 7100 during deployment of the inflator 720. The initiation assembly 7100 may alternatively be positioned in the secondary gas chamber 768. The initiation assembly 7100 may additionally comprise a burst disc, such as burst disc 778c, positioned over the initiator aperture 7102.

The initiation assembly 7100 may include an initiator 7104, which is an electrically-triggered pyrotechnic device. The initiator 7104 may, for example, have a head 7106, a body 7108 containing pyrotechnic material, and electrical prongs 7110 through which the activation signal is received. The body 7108 may be seated within an initiator retention member 7112. The prongs 7110 may be inserted into a plug (not shown) of the electric line 731 leading to the accelerometer 711 or the controller (not shown).

If desired, the initiation assembly 7100 may also have a quantity of booster material 7116 that intensifies the thermal energy provided by the initiator 7104. The

booster material 7116 may be separated from the initiator 7104 by a dome 7118 designed to rupture, or even disintegrate, upon activation of the initiator 7104. Alternatively, the booster material 7116 may be housed within the initiation assembly 7100 itself. The initiation assembly 7100 may also have a housing 7119 that encases and protects the booster material 7116 and the initiator 7104. If desired, the housing 7119 may effectively isolate the initiator 7104 and the booster material 7116 from the pressure within the primary gas chamber 766.

The inflator 720 may be of any type, including pyrotechnic, compressed gas, and hybrid types. In the inflator of Figure 17, the inflator 720 is a hybrid type inflator, with the pyrotechnic inflator and booster material 7116 as well as a gas-producing material (or "gas generant") 784 in a compressed state. Due to the compression, the gas-producing material 784 may exist in the form of a gas 785 as well as a liquid 786 within the primary gas chamber 766. Alternatively, in a pyrotechnic inflator, the gas-producing material may not be an inert compressed liquid, gas, or mixture, but may take the form of a combustible solid or liquid.

With the inert, compressed, gas-producing material 784 of Figure 17, the initiation assembly 7100 deploys within milliseconds to produce heat that causes expansion of the gas-producing material 784. The result is a sudden pressure shock and/or pressure increase within the gas chamber 766. The pressure shock and/or increase dislodges the burst disc 778c from the initiator aperture 7102 as well as the burst discs 778a, 778b to open the first and second exit orifices 770,772 and allow the first and second primary gas flows 794a, 794b to escape. As the inflation gas flows out of the inflator 720, the liquid 786 is vaporized to add to the volume of the primary gas flows 794a, 794b. The gas-producing materials 784b present in the secondary gas chamber 768 next begin to exit the inflator 720, thus causing the secondary gas flow 796. As a result, a considerable amount of gas can be produced by the inflator 720 over a controllable time period despite its modest size.

The use of the liquid gas producing material 786 may be beneficial because the liquid 786 will absorb heat as it vaporizes. Hence, the primary and secondary gas flows 794a, 794b, and 796 will be cool relative to other inflation gases or even possibly ambient air, and therefore less likely to damage the inflatable curtain 710. The inflatable curtain 710 may therefore be made from a comparatively less heat-resistant and quite possibly cheaper material. For example, a thinner silicon coating for the fabric of the inflatable curtain 710 may be sufficient to protect the fabric from thermal damage. Additionally, as

the gas 785 resulting from the liquid 786 begins to warm to ambient temperatures, it expands, thus extending the period of time for which the curtain 710 remains inflated and capable of providing protection to a vehicle occupant.

The inflator 720 is seen to be inexpensive and easy to manufacture in comparison to many other airbag inflators. The primary gas chamber 766 may first be formed through known methods. If desired, the primary gas chamber 766 may be provided as a single unitary piece, as depicted in Figure 17. The burst discs 778a, 778b and/or the gas- producing material 784 may, for example, be inserted through the assembly aperture 7101.

The gas-producing material 784 may alternatively be inserted cryogenically, i. e., frozen and compressed into solid form and inserted through a fill opening 788 which may later be sealed with a fill opening seal 789. The initiation assembly 7100 may then be inserted into the secondary gas chamber 768 with the assembly aperture 7101 oriented inwardly, and welded in place, for example, through laser welding.

In the alternative to one-piece construction, the gas chamber 766 may be formed as two separate pieces to facilitate the insertion of the burst discs 778a, 778b, the initiation assembly 7100, and the gas-producing material 784. For example, the first end 771 may be separated from the remainder of the gas chamber 766 by a radial seam (not shown), so that the first end 771 and the remainder of the gas chamber 766 form a tube with a circular opening. The burst disc 778a, the initiation assembly 7100, and/or cryogenic material may easily be inserted into such circular openings and fixed in place. The first end 771 may then be attached, for example, through welding, to the remainder of the gas chamber 766.

This process could be repeated for second end 773.

Many other aspects of the inflator 720 may be varied to suit the geometry of the vehicle 712. the size and shape of the inflatable curtain 710, and the available manufacturing equipment. Figure 18 presents an alternative dual flow biaxial inflator, containing a number of variations from the inflator 720 of Figures 16 and 17. These variations may be used in any combination, or in conjunction with other variations that will be recognized by those of skill in the art, to produce a larger number of embodiments of the invention than can be illustrated or specifically described herein.

Referring to Figure 18, an inflator 7120 according to one alternative inflator of the invention is shown. The inflator 7120 may have a first primary gas chamber 7166a designed to be installed within an inflation port of an inflatable curtain in much the same manner as the gas chamber 766 of Figure 17. This first primary gas chamber 7166a also

has an initiation assembly 7100 for activating the inflator 7120. The inflator 7120 further includes a second primary gas chamber 7166b, which may be substantially identical to the first primary gas chamber 7166a. The inflator 7120 further has a secondary gas chamber 7168 attached to the first and second primary gas chambers 7166 by flow restrictors 7180a, 7180b. This secondary gas chamber 7168 may be segregated from the primary gas chambers 7166a, 7166b by frangible seals such as burst discs 7178c, 7178d, respectively, positioned against flow restrictors 7180a, 7180b.

In inflator 7120, the primary gas chambers 7166a, 7166b are attached to the first and second inlet ports 760,762 of the curtain (not shown), and sealed to prevent gas escape. The first primary gas chamber 7166a contains a gas producing material 7184a, which may include a gaseous reagent such as a pressurized gas 7185a, and a liquid reagent such as a liquefied gas 7186a. These gas-producing materials 7184a are sealed in primary gas chamber 7166a by a frangible seal. In Figure 18 this seal is omitted for clarity in this figure.

The inflator 7120 is configured, as inflator 720 of Figure 16, to produce first and second primary flows of gas 7194a, 7194b which pass out of the first and second primary gas chambers 7166a, 7166b through the exit orifices 7172,7170 and the exit nozzles 7192a, 7192b into the curtain (not shown).

As briefly noted above, the inflator 7120 includes first and second initiation assemblies 7100a, 7100b attached to primary gas chambers 7166a, 7166b at assembly apertures 7101 a, 7101 b. The initiation assemblies 7100a, 7100b include an initiator aperture 7102 through which the heat and other combustion products from the initiation of the initiator 7104 pass after the initiation of the initiator 7104. The initiation assemblies 7100a, 7100b further include a head 7106, a body 7108, and prongs 7110 for connecting the initiator 7104 with the electronic system (not shown), including the accelerometer (not shown), of the vehicle. The initiator 7104 is retained by an initiator retention member 7112 and a housing 7119 to keep the initiator in place. The initiator may also have booster material (not shown) contained in a dome (not shown) near the initiator 7104 in order to aid in the production of the primary flows of gas 7194. Finally, the initiator assemblies 7100a, 7100b may further include burst discs 7178e, 7178f, respectively, which cover the initiator apertures 7102 prior to the initiation of the inflator.

The inflator 7120 of Figure 18 further includes flow restrictors 7180a, 7180b which join the first primary gas chamber 7166a with the secondary gas chamber 7168, and

join the second primary gas chamber 7166b to the secondary gas chamber 7168. Here, the flow restrictors 7180a, 7180b may take the form of restricted flow channels 7179. Such a restricted flow channel 7179 may be similar to a capillary tube. The restricted flow channel 7179 further includes a narrow flow restrictor orifice 7182 that limits the rate at which the inflation charge housed in the secondary gas chamber 7168 may escape. The flow channel 7179 is defined by a flow restrictor orifice radius 7181 and a flow restrictor orifice diameter 7183.

The secondary gas chamber 7168 is configured to provide a secondary flow of gas 7196 into the first and second primary gas chambers 7166a, 7166b, and subsequently into the inflatable curtain (not shown). The secondary gas chamber 7168 is linked to the first and second primary gas chambers 7166a, 7166b through the flow restrictors 7180a, 7180b.

The primary gas chambers 7166a, 7166b may also include a fill opening 788 and a fill opening seal 789 for filling the primary gas chambers 7166a, 7166b with a gas producing material 7184a, 7184b, which may, as in the inflator 720 of Figures 16 and 17, include a gaseous gas producing material 7185a, 7185b. The secondary gas chamber may include such a material and/or a liquid gas producing material 7186 such as a liquefied gas. In inflator 7120, since the first and second primary gas chambers 7166a, 7166b are separated from the secondary gas chamber 7168 by the burst discs 7178a, 7178b and their associated structures, including the interior cap 7174 and the burst disc retaining member 7190, the gas chambers 7166a, 7166b, and 7168 may include different gas producing materials 7184a, 7184b, and 7184c.

As briefly stated, the flow restrictors 7180a, 7180b may be associated with a burst disc 7178a, 7178b and accompanying interior caps 7174a, 7174b. The burst discs 7178a, 7178b are positioned over openings 7176a, 7176b and are held in position against interior caps 7174a, 7174b by the pressurized contents of the secondary gas chamber 7168. The secondary flow restrictors 7180a, 7180b may also contain burst disc retention members 7190a, 7190b that, as described above, contain the retention member after initiation of the inflator to prevent ejection of the discs and any potential accompanying damage.

In use, the inflator of the invention may be configured to provide a primary flow of gas and a secondary flow of gas. The primary flow of gas is generated from a gas generant supply placed within the primary gas chamber. This primary flow of gas is initiated either directly by an initiator assembly placed within the primary gas chamber or indirectly by an initiator assembly placed within the secondary gas chamber. The initiation of the device

ruptures the frangible seal of the primary gas chamber and heats the gas generant of the primary gas chamber, thus causing gas formation and gas flow from the primary gas chamber. This primary flow of gas is then split into first and second primary flows of gas as it passes through the first and second exit orifices of the primary gas chamber or chambers, and preferably channeled into an attached airbag such as an inflatable curtain.

Following the primary flow of gas, a secondary flow of gas may be initiated. This flow may be initiated passively in inflators where the flow restrictor, though sufficiently narrowed to meter the flow of gas, has no complete blockage. Such a passive initiation occurs when the initiator has fired and the primary gas chamber has begun to empty, thus decreasing the pressure in the primary gas chamber. Passive initiation may also be achieved when the secondary gas chamber includes a pressure sensitive frangible seal such as a burst disc configured to rupture at a specific pressure gradient. In such an inflator, the gas generants housed in the primary and secondary gas chambers would be pressurized.

Upon partial emptying of the primary gas chamber after initiation of the primary gas flow, the pressure gradient between the high pressure of the secondary gas chamber and the decreasing pressure of the primary gas chamber would be sufficient to rupture the seal and initiate the secondary gas flow.

Alternatively, an initiator placed in each gas chamber may initiate both the primary and secondary flows of gas. In such an inflator, a frangible seal may be associated with the secondary gas chamber to prevent early escape of the gas generants stored within the secondary gas chamber. In these inflators, the initiators may be optionally connected to a controller which may control the initiation of the primary gas chamber separately from the initiation of the secondary gas chamber. Such inflators may thus be enabled to function in a manner adjustable to the individual circumstances of a given collision."Smart"inflators such as these may be tuned to fire only the first initiator and cause only the primary flow of gas in minor collisions. Additionally, such inflators could be tuned to detect severe collisions and fire each initiator at adjustable intervals to assure sufficient extended inflation of the inflatable curtain or airbag connected to the inflator to protect a vehicle occupant. Such function would be especially useful in rollover collisions, which could be detected by the controller module and responded to by firing both initiators in sequence so as to provide an extended flow of inflation gas and thus an airbag that is supportive over an extended period of time relative to conventional airbags. Finally, the controller could be configured to initiate a secondary flow of inflation gas to completely reinflate the airbag

using the inflation charge of the secondary gas chamber in response to a second collision occurring shortly after the triggering collision, or on the occurrence of some other suitable event.

The dual stage inflators of the present invention thus provide a significant advancement in airbag design. Through the addition of the secondary gas chamber, the use of the flow restrictor, and the refinement of exit orifice designs, airbag systems may be produced and installed with less time and expense. Furthermore, the use of axial flow exit orifices and secondary gas chambers with flow restrictors enables a single inflator to rapidly and uniformly provide inflation gas for an airbag possibly comprising multiple protection zones, and then to maintain an inflation pressure sufficient to protect a vehicle occupant over a period of time. This inflation pressure may be maintained using methods such as providing a secondary stream of inflation gas to the airbag. The inflators of the invention may also include a primary inflation flow of gas generated from a liquefied gas.

Due to the latent heat of vaporization of the liquid gas, the inflation flow of gas would be cooler than the ambient air surrounding the airbag. The cool inflation gas would then warm and expand, thus reinforcing the inflation pressure of the airbag.

As explained above, such airbag inflators yielding extended gas flow are especially important in rollover collisions in which lateral protection of a vehicle occupant is needed for periods of time that exceed those protection periods required or even desired in ordinary airbag applications. Such extended time periods may range from five seconds to eight seconds to even twenty seconds. The provision of an airbag inflator that makes such extended inflation possible is an improvement in the art.

The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.