WO2000021799A9

WO2000021799A9 - Flow regulated inflator

Info

Publication number: WO2000021799A9
Application number: PCT/US1999/023707
Authority: WO
Inventors: Michael Fink
Original assignee: Airbelt Systems Llc
Priority date: 1998-10-09
Filing date: 1999-10-08
Publication date: 2000-09-21
Also published as: AU1312900A; WO2000021799A1

Abstract

A spool valve (304) controls the release of gas from a pressure vessel (50) into an airbag upon the release of the gas in the event of a collision. The valve (304) uses pilot pressure acting on either end of the spool (308) to actuate the spool (308). The position of the spool (308) within the valve (304) determines the flow rate through the valve (304).

Description

Flow Regulated Inflator

Related Application Data

The present application is a continuation-in-part of commonly owned, co-pending application for patent, entitled Airbag System Inflator, Serial No. 08/656,374, filed March 21, 1996, now United States Patent No. 5,820,162, issued October 13, 1998.

Background of the Invention

Field of the Invention

The present invention relates generally to a motor vehicle inflatable restraint system, and more particularly to an inflator having a pilot valve to control the flow of pressurized gas from a high pressure vessel into an air bag of the inflatable restraint system.

Background of the Art

Inflatable restraint systems to protect motor vehicle occupants from injury in the event of a collision have been incorporated into motor vehicles in response to enacted legislation and public demand for safer motor vehicles. Air bags have been widely demonstrated to be highly effective in motor vehicle frontal collisions by reducing the degree of injury to passengers of vehicles equipped with such systems. In a typical inflatable restraint system, as is well known in the art, an airbag inflates upon detection of sudden deceleration indicative of a frontal collision to protect the passengers of the vehicle from forceful contact with hard surfaces in the vehicle interior. Typically, in new motor vehicles the inflatable restraint system is installed in the hub of the steering wheel for driver protection with an additional inflatable restraint system being installed in the dashboard for front seat passenger protection becoming increasing popular as standard equipment. Inflatable restraint systems have also been installed in the doors of motor vehicles to protect against side impact collisions, in the seat backs of the front seats to protect rear seat passengers in the event of a frontal collision, and in the headrest portion of the seats to provide full head protection in any type of collision..

The typical inflatable restraint system includes an inflator, an airbag, deceleration or impact sensors and triggering electronics. The air bag is a folded, expansible bag constructed of suitable fabric. The inflator is connected to the interior of the air bag. The most common inflator in use in motor vehicles is of the pyrotechnic type which contains a solid propellant, such as sodium azide. Upon impact being detected by the sensors, the triggering circuit ignites the sodium azide propellant, which in turn rapidly generates a hot gas discharge filling and inflating the air bag. As the air bag inflates, it escapes from its enclosure and expands, for example, in front of the driver, cushioning the driver as the driver is thrown forward by the impact and prevents the driver from striking the hard interior surface of the vehicle.

Although hot gas inflators currently command a 100% market share for motor vehicle inflatable restraint systems, the limitations and disadvantages associated with inflating an air bag with the hot gas from sodium azide and other types of pyrotechnic inflators are well known and documented in the art. Sodium azide is a known hazardous toxic chemical. In addition, when the air bag is inflated, gas at very high temperatures is released that can inflict severe burns to the occupant. Other limitations and disadvantages of the pyrotechnic inflator technologies include explosions, transportation concerns, environmental issues, and chemical degradation. Accordingly, there is a need for an inflatable restraint system that is not dependent upon a pyrotechnically generated hot gas.

There is known in the prior art a compressed source "cold gas" inflator which does not use a pyrotechnically ignited solid propellant. In an inflatable restraint system using a cold gas inflator, pure stored compressed gas is released to inflate the air bag. Although initial research and development of inflatable restraint system focused on both cold gas and hot gas inflators, a major limitation of the prior art cold gas inflator that has prevented it from being incorporated into vehicles is that the output of the cold gas inflator is unacceptably affected by ambient temperature extremes. Any airbag inflator, cold gas or hot gas, is required to function in temperatures ranging from -40° C (-40° F) to 98° C (208° F), which are possible extremes encountered in various locations during winter extremes to hot summer conditions.

For a compressed gas contained in a fixed volume, it is well known that the gas pressure increases or decreases in proportion to the ambient temperature, as set forth by the Ideal Gas Law: Pι/P =-T*/T . For example, a vessel pressurized to 6000psi @ ambient temperature (70° F) would have its internal pressure affected by temperature extremes as follows:

@ -40° F, internal pressure = 4755psi @ 208° F, internal pressure = 7570psi. The above example shows how the temperature extremes affect the storage pressures and thus, will affect the total outflow of gas volume that will inflate the airbag. As a result of this large variance in vessel pressure, a cold gas inflator, designed to fill the airbag to proper proportions at the high temperature conditions, would fill the airbag to only a portion of the desired level during the cold extreme conditions, thus, producing insufficient energy absorbing characteristics for the occupant of the vehicle during an impact. Conversely, if the cold gas inflator was designed to have proper bag filling characteristics at the low temperature extremes, in a high temperature environment the bag would fill to an unacceptably high pressure level possibly causing tearing at the seams or a burst, resulting in loss of energy absorption of the occupant. Alternatively, if the airbag did not burst, the higher pressure would produce an unacceptably very "hard" air bag, possibly causing injury to the occupant of the vehicle when in forceful contact with the air bag. Both of these extreme situations are unacceptable limitations and disadvantages of the prior art.

Because of these foregoing described limitations and disadvantages of the prior art cold gas inflator that the early development work in inflatable restraint systems favored the hot gas inflator despite the know problems associated with solid propellants used in the hot gas inflator. Although the solid propellant combustion process is also affected by temperature extremes, the affect is orders of magnitude less than in the pure stored gas inflators. One prior art device, known as the hybrid inflator, uses both a compressed source, which is affected by temperature extremes to the same degree as a stored gas inflator, and a solid propellant to mitigate the effects of ambient temperature, has been developed but has not been commercially accepted. In the hybrid inflator, the solid propellant is used to assist in the total gas output which varies less with temperature. Therefore, the overall temperature dependent pressure variance of the hybrid design is less than the conventional pure stored gas design. However, the cost of the hybrid inflator is much greater than either the hot gas or the cold gas inflator since it incorporates the inflation mechanism from each. Accordingly, the hot gas inflator has become the commercially accepted prior art device because it was initially demonstrated to reduce these temperature dependent pressure variances to acceptably low levels and offer the greater overall performance and occupant protection.

Another limitation associated with the prior art cold gas inflator is that its output flow of gas during the initial vessel opening is, by nature, very violent and aggressive. When the gas is released unregulated into the air bag it can cause high stress induced loading in the bag itself or to the occupant, if the occupant is close to the air bag as it deploys. It is important, therefore, to provide some means of regulating the gas from the compressed gas source into the air bag during the initial vessel opening stage.

A limitation in general that extends to all inflatable restraint systems is that the inflator is designed to pressurize the airbag independent of the ambient environment or other variables, conditions and parameters which exist during a collision. An example of possible crash variables, conditions and parameters are as follows:

-Crash Severity

-Ambient Temperature

-Occupant Weight

-Occupant Position

-Seat belt Fastened/Unfastened. For example, design guidelines for commercially available inflatable restraint systems are provide the maximum protection for the unbelted 50th percentile male (which represents the median size and weight of the population of drivers) at a 30 mph crash speed into a rigid barrier (the "ideal crash").

The presently available inflators will deploy the airbag to the same magnitude in every crash with no dependence on any of the previously mentioned variances which occur in all crashes. Therefore, an occupant whose size and weight is considerably different from this median range will experience less than ideal decelerating characteristics from the airbag. The smaller and lighter occupant will have a tendency to rebound off the airbag, where injury and even death from this rebound is typical. Deaths caused to infants and small children from the deployment of airbags are the current focus of media inquiry. The larger and heavier occupant can deflate the entire bag, and with the remaining energy impact the steering wheel or dashboard causing injury which the ideal size and weight occupant would not otherwise suffer.

Commercial available inflatable restraints must employ a very aggressive of the airbag which must be fully inflated in approximately 30-60 milliseconds, depending on location in the vehicle, in order to provide the proper energy absorbing characteristics to the occupant. Because of its high deployment forces, an airbag has the potential to cause great harm in non-ideal crash conditions. During a moderate crash condition with a small occupant, it would be undesirable for the airbag to deploy with its normal high force, as the occupant interaction with the airbag would cause injury from the deployment. However, a great majority of the crashes in real world accidents are not the "ideal crash." There has been several recent attempts to address the above identified limitations and disadvantages of the prior art inflators. For example, to protect small children from being severely injured or killed form airbag deployment, it has been proposed to provide the vehicle with a defeat switch to disable the inflatable restraint at the location where the child is seated. However, this solution is unacceptable since the child will be exposed to even greater risk of injury or death by being unprotected from striking hard surfaces of the vehicle interior during a collision. Furthermore, the effectiveness of the inflatable restraint system in protecting adults will be seriously comprised should the operator forget to enable the inflatable restraint system for the protection of adult occupants.

Another example of a recent attempt to address the above identified limitations and disadvantages of the prior art inflators is to provide a dual stage in conjunction with weight sensors to detect the weight of the occupant proximate the airbag. If the weight sensor detects the occupant weight below a threshold weight, only one stage will deploy, thereby reducing inflation pressure yet providing sufficient energy absorbing protection to the small occupant. However, the dual stage inflator effectively doubles the cost of the inflator since two separate sources of solid propellant or cold gas are required along with dual triggering electronics.

Yet another example of a recent attempt to address the above identified limitations and disadvantages of the prior art inflators is to provide a mechanical valve at the output of the inflator in conjunction with various sensors which detect one or more of the variables, conditions or parameters described above. A logic circuit or processor may then detect the sensor conditions and command an actuator or motor to adjust the valve element thereby controlling the flow rate at the output of the inflator and the inflation rate and pressure of the deployed airbag. Theoretically, such a system could adjust for any of the variables, conditions or parameters in real time from before and after the onset of the collision. However, the reliability and operability of such a system in real world crashes has not been demonstrated. For example, the collision may destroy the logic or processor electronics or the mechanical valve may become physically deformed by the collision forces, in either event causing a failure of the inflatable restraint system.

Accordingly, there is a need for an inflatable restraint system that overcomes on or more limitations and disadvantages of the prior art discussed hereinabove. Specifically there is a need for a cold gas inflator which is temperature compensating. Additionally there is a need for a cold gas inflator which regulates the output pressure and inflation rate of the airbag. Furthermore, there is a need for a cold gas inflator which provides a valve without any need for external circuits or actuators to achieve variable inflation rates.

Summary of the Invention

It is therefor an object of the present invention to provide a cold gas inflator which overcomes one or more limitations and disadvantages of the prior art inflators.

It is a further object of the present invention to provide a cold gas inflator which is temperature compensating.

It is another object of the present invention to provide a cold gas inflator which regulates the output pressure and inflation rate of the airbag.

It is yet another object of the present invention to provide a cold gas inflator which includes a valve without any external circuit or actuator to achieve variable inflation rates.

According to the present invention, an inflator comprises a vessel to store an immediately releasable pressurized gas and a valve including a housing and a moveable member. The housing has an internal chamber, an inlet orifice and an outlet orifice. Each of the inlet orifice and the outlet orifice are in fluid communication with the chamber to define a flow path from the inlet orifice to the outlet orifice through the chamber. The inlet orifice is adapted to receive the gas from said vessel upon release of the gas. The moveable member is disposed within the chamber and is normally biased in an initial position. The moveable member has a first end, a second end, an outer portion disposed in slideable engagement with the housing and an open portion disposed in the flow path. The moveable member defines a first volume in the chamber between the housing and the first end and a second volume in said chamber between the housing and the second end wherein a selected one of the first volume and the second volume is in fluid communication with the flow path. The outer portion is disposed in a partially restrictive arrangement with a portion of at least one of the inlet orifice and the outlet orifice to determine an initial cross sectional area of said flow path. The moveable member is controllably displaced in response to pressurized gas being present in the flow path and communicated at a preselected rate into a selected one of the first volume and the second volume to develop a pressure differential between the first volume and the second volume. The moveable member is displaced from the initial position in response to the pressure differential. The portion of the at least one of the inlet orifice and the outlet orifice in the restrictive arrangement with the outer portion is varied upon displacement of the moveable member thereby varying the cross sectional area of the flow path.

An feature of the present invention is that the moveable member of the valve is responsive to pressure differentials developed when the gas is released from the vessel. An advantage over the prior art is that valve operation does not depend upon external electronic circuits or actuators which may be damaged during a collision.

These and other objects, advantages and features of the present invention will become readily apparent to one skilled in the art from a study of the following description of the preferred embodiment when read in conjunction with the attached Drawing an appended Claims.

Brief Description of the Drawing

Figure 1 is a cut away view of the inflator constructed according to the principles of the present invention.

Figure 2 is an enlarged view of Figure 1.

Figure 3 illustrates an alternative embodiment of the inflator of the present invention.

Figure 4a-e is an enlarged cut away view of the valve illustrating its operation..

Figure 5 is a side view illustrating utility of the inflator of the present invention.

Figure 6 is a view similar to Fig. 5 showing an alternative location.

Figure 7 is a schematic of a control circuit responsive to input variable conditions in the environment of the inflator.

Figure 8 is an airbag PSI curve.

Figure 9 is a cut away view of an alternative embodiment of the present invention.

Figure 10 is a side cut away vies of an alternative embodiment of the spool and spool cavity.

Figure 11 is an yet another alternative embodiment of an inflator constructed according to the principles of the present invention.

Description of the Preferred Embodiment The description of the Figures 1-10 is set forth in commonly owned, co-pending application for patent, entitled Airbag System Inflator, Serial No. 08/656,374, filed March 21, 1996, now United States Patent No. 5,820,162, issued October 13, 1998, which is incorporated by reference herein for all it contains.

With reference to Fig.'s 1-4 and Fig. 11, there is shown an inflator 300 constructed according to the principles of the present invention. Inflator 300 includes a source 302 of immediately releasable gas, and a valve 304 having a housing 306 and a moveable member 308. Although the best mode embodiments of the present invention herein described are particularly described in conjunction with a cold gas inflator, the principles to the present invention are also applicable to a hot gas inflator and a hybrid inflator.

For the cold gas inflator embodiment, the source 302 contains and stores the gas 52, preferably inert, under pressure within the vessel 50 constructed to withstand the required gas pressure as is known in the art. The gas 52 is contained and sealed within the vessel 50 by a burst disk 48. To make the gas stored within the vessel 25 immediately releasable from the inflator 300, the detonator, also referred to herein as an initiator, 46 is provided. The initiator 46, for example a squib, may detonate in response to an electrical signal applied thereto along a wire 310. The detonation of the initiator 46 in turn ruptures the burst disk 48. Rupture of the burst disk 48 initiates of flow of gas through the valve 304 and its immediate release from the inflator 300.

For the hot gas inflator embodiment the source 302 may contain within the vessel 50 a combustible substance, as a well-known the art, which substance upon ignition develops a gas causing gas pressure to immediately build within the vessel 50 and initiate a flow of gas through the valve 304 and its immediate release from the inflator 300. In such hot gas embodiment, the burst disk 48 is not required and the electrical signal on the wire 310 used to detonate the initiator 48 present in the cold gas embodiment may instead be utilized to ignite the combustible substance in the hot gas embodiment. The vessel 50 must also then be constructed to withstand the ignition of the combustible substance.

The housing 306 has an internal chamber 312, an inlet orifice 314 and an outlet orifice 316. Each of the inlet orifice 314 and the outlet orifice 316 are in fluid communication with the chamber 312 to define a flow path 317 from the inlet orifice 314 to the outlet orifice 316 through the chamber 312. The inlet orifice 314 is adapted to receive the gas from source 312 upon release of the gas. The moveable member 308 is disposed within the chamber 312 and is normally biased in an initial position. The moveable member 308 has a first end 318, a second end 320, an outer portion 322 disposed in slideable engagement with the housing 306 and an open portion 324 disposed in the flow path 317. The moveable member 308 defines a first volume 326 in the chamber 312 between the housing 306 and the first end 318, and a second volume 328 in the chamber 312 between the housing 306 and the second end 320. A selected one of the first volume 326 and the second volume 328 is in fluid communication with the flow path 317. The outer portion 322 is disposed in a partially restrictive arrangement with a portion of at least one of the inlet orifice 314 and the outlet orifice 316 to determine an initial cross sectional area of the flow path 317. The moveable member 308 is controllably displaced in response to pressurized gas being present in the flow path 317 and communicated at a preselected rate between a selected one of the first volume 326 and the second volume 328 to develop a pressure differential between the first volume 326 and the second volume 328. The moveable member 308 is displaced from the initial position in response to the pressure differential, such that the portion of the at least one of the inlet orifice 314 and the outlet orifice 316 in the restrictive arrangement with the outer portion 322 is varied upon displacement of the moveable member 308 thereby varying the cross sectional area of the flow path 317.

In the embodiment of Fig.'s 1-4, the valve 304 further includes a first pilot orifice 330 disposed within a selected one of the moveable member 308 and the housing 306. The first pilot orifice 330 is interposed the flow path 317 and the first volume 326 to communicate the pressurized gas when present in the flow path 317 to the first volume 326 such that pressure increases in the first volume 326 to move the moveable member 308 in a direction toward the second volume 328. The diameter of the first pilot orifice is selected to control the rate of displacement of the moveable member 308 In a preferred embodiment, the first pilot orifice 330 is disposed in the moveable member 308.

The valve 304 may further include a second pilot orifice 332 interposed the flow path 317 and the second volume 328 to communicate the pressurized gas when present in the flow path 317 to the second volume 328 such that pressure increases in the second volume 328 to impede displacement of the moveable member 308 in a direction toward the second volume 328. The diameter of the second pilot orifice 332 is selected to control the rate of impediment of the moveable member 308. In a preferred embodiment the second pilot orifice is disposed in the moveable member 308. The housing 306 may also include a vent orifice 334 to communicate gas in the second volume 328 external of the housing 306 to bleed pressure therefrom.

In a particular preferred embodiment, the moveable member 308 may be a spool 336 having a generally cylindrical outer portion 338 in axial slideable engagement within the chamber 312 and an indented portion 340 within the flow path 317. As best seen in Fig.'s 2-4, the first pilot orifice 330 and the second pilot orifice 332 may each be preferably disposed in the spool 336.

In the embodiment of Fig. 11, the valve includes a first pilot orifice 342 disposed within a selected one of the housing 306 and the moveable member 308. The first pilot orifice 342 is interposed the flow path 317 and the second volume 328 to communicate the gas from the second volume 328 to the flow path 317 such that pressure decreases in the second volume 317 to move the moveable member 308 in a direction toward the second volume 328. The diameter of the first pilot orifice is selected to control the rate of displacement of the moveable member 308.

In this embodiment the valve 304 is disposed within the reservoir chamber 344 of the vessel 50. The valve 304 may further include a second pilot orifice 366 interposed the first volume 326 and the reservoir chamber 344 to communicate the pressurized gas from the reservoir chamber 344 to the first volume 326 when the outlet orifice 316 is closed. The second pilot orifice 346 has a diameter substantially less than a diameter of the first pilot orifice 342. In a particular preferred embodiment, the first pilot orifice 342 is disposed in the moveable member 308 and the second pilot orifice 346 is disposed in the housing 306.

In the inflator 300 of either embodiment, but as best seen in Fig 11, the valve 304 may further include a single spring 348 disposed in the second volume 328 interposed the housing 306 and the moveable member 308 to bias the moveable member 308 in an initial position toward the first volume 326. More particularly, the second end 320 of the moveable member has a bore 350 and the housing 306 has a bore 352 coaxial with and facing the bore 350 of the moveable member 308. The spring 348 is disposed in each of the bores 350, 352. The internal chamber 312 may have an annular lip 354. The moveable member 308 abuts the lip 354 when in the initial position.

With reference to Fig. 7, there is shown a circuit 360 responsive to a present state of input variable conditions in the environment of the inflator 300. These input variable conditions may include deceleration, seatbelt status, PSI of the vessel 50, occupant position and occupant weight, all of which may be detected by a respective one of deceleration sensor 362, seatbelt sensor 364, PSI sensor 366, occupant position sensor 368 and occupant weight sensor 370, such sensors responsive to these conditions being known. Upon detection of sudden deceleration indicative of a collision, the deceleration sensor 362 develops a deceleration signal which may be digitized and applied to a processor 372 of the circuit 360. The processor 362, in response to the deceleration signal develops the hereinabove mentioned electrical signal along wire 310 for application to the initiator 46.

In the presence of certain conditions, it is desirable to terminate inflation of the airbag 30 prior to all of the gas being released from the source 300, or to accelerate the rate of inflation. Accordingly, the housing 306 may further include an opening 374 to communicate a selected one of the first volume 326 and the second volume 328 external of the housing 306, and an electrical signal responsive device 376, such as a squib, sealingly disposed in the opening 374. If the opening 374 is adjacent the first volume 328, removal of the device 376 will tend to restrict flow as seen in Fig. 4E. Conversely, if the opening is adjacent the second volume, removal of the device will allow the valve 304 to be opened rapidly, for the embodiment of Fig. 3. In either event, the dynamic position of the moveable member 308 may be changed subsequent of release of gas from the source 300 to establish a different flow rate through the flow path 317 by changing the effective cross sectional area thereof. This different flow rate may have a value preselected to exist upon the real time present state of the variable conditions detected by each of the sensors 362, 364, 366, 368, 370. Furthermore, a RAM 380 may also contain a lookup table for comparing the deceleration signal to stored deceleration values indicative of crash intensity.

The processor 372 is responsive to the signal from each of said sensors to develop a further electrical signal along a wire 378 for application to the device 376. The signal along wire 378 is developed as a function of the signals developed by each of the sensors 362, 364, 366, 368, 370, all or any of which may be utilized in any combination. The processor is programmed with suitable algorithms to develop the signal along wire 378 as a function of the sensor signals. An example of such control of the inflator 300 from such real time variable conditions may be found in U.S. Patent No. 5, 439, 249.

There has been described hereinabove exemplary preferred embodiments of a vortex valve inflator constructed according to the principles of the present invention. Those skilled in the art may now make numerous uses of, and departures from, the hereinabove described embodiments without departing the inventive concepts disclosed herein. Accordingly, the present invention is to be construed solely by the scope of the appended claims and their permissible equivalents.

Claims

The ClaimsWhat is claimed as my invention is:

1. An inflator comprising: a of an immediately releasable gas; and a valve including a housing and a moveable member, said housing having an internal chamber, an inlet orifice and an outlet orifice, each of said inlet orifice and said outlet orifice being in fluid communication with said chamber to define a flow path from said inlet orifice to said outlet orifice through said chamber, said inlet orifice being adapted to receive said gas from said source upon release of said gas; and said moveable member being disposed within said chamber and being normally biased in an initial position, said moveable member having a first end, a second end, an outer portion disposed in slideable engagement with said housing and an open portion disposed in said flow path, said moveable member defining a first volume in said chamber between said housing and said first end and a second volume in said chamber between said housing and said second end wherein a selected on of said first volume and said second volume is in fluid communication with said flow path, said outer portion being disposed in a partially restrictive arrangement with a portion of at least one of said inlet orifice and said outlet orifice to determine an initial cross sectional area of said flow path, said moveable member being controllably displaced in response to pressurized gas being present in said flow path and communicated at a preselected rate between a selected one of said first volume and said second volume to develop a pressure differential between said first volume and said second volume, said moveable member being displaced from said initial position in response to said pressure differential, said portion of said at least one of said inlet orifice and said outlet orifice in said restrictive arrangement with said outer portion being varied upon displacement of said moveable member thereby varying said cross sectional area of said flow path.

2. An inflator as set forth in Claim 1 wherein said valve further includes a first pilot orifice disposed within a selected one of said moveable member and said housing, said pilot orifice being interposed said flow path and said first volume to communicate said pressurized gas when present in said flow path to said first volume such that pressure increases in said first volume to move said moveable member in a direction toward said second volume, the diameter of said pilot orifice being selected to control the rate of displacement of said moveable member.

3. An inflator as set forth in Claim 2 wherein said valve further includes a second pilot orifice interposed said flow path and said second volume to communicate said pressurized gas when present in said flow path to said second volume such that pressure increases in said second volume to impede displacement of said moveable member in a direction toward said second volume, the diameter of said second pilot orifice being selected to control the rate of impediment of said moveable member.

4. An inflator as set forth in Claim 3 wherein said housing includes an vent orifice to communicate gas in said second volume external of said housing to bleed pressure therefrom.

5. An inflator as set forth in Claim 3 wherein said moveable member is a spool having a generally cylindrical outer portion in axial slideable engagement within said chamber and an indented portion within said flow path.

6. An inflator as set forth in Claim 5 wherein said second pilot orifice is disposed in said spool.

7. An inflator as set forth in Claim 5 wherein said first pilot orifice is disposed in said spool.

8. An inflator as set forth in Claim 3 wherein said second pilot orifice is disposed in said moveable member.

9. An inflator as set forth in Claim 2 wherein said first pilot orifice is disposed in said moveable member.

10. An inflator as set for in Claim 1 wherein said housing includes an opening to communicate a selected one of said first volume and said second volume external of said housing and an electrical signal responsive device sealingly disposed in said opening, said inflator further comprising: a circuit responsive to a present state of input variable conditions in the environment of said restraint system to develop a first electrical signal for application to said device upon the occurrence certain ones of said variable conditions, said device being at least partially removed from said opening in response to said electrical signal to move said movable member to a dynamic position at which flow path has a cross sectional area to establish a reduced flow rate through said flow path at a value preselected to exist upon the real time present state of said variable conditions.

11. An inflator as set forth in Claim 10 wherein said circuit includes: a plurality of sensors, each of said sensors responsive to a respective one of said variable conditions, each of said sensors developing a second electrical signal as a function of said respective one of said variable conditions; a processor responsive to said second signal from each of said sensors to develop said first electrical signal as a function of said second electrical signal from each of said sensors; a device responsive to said second electrical signal to cause actuation of said movable member to said dynamic position.

12. An inflator as set forth in Claim 10 wherein said opening communicates said first volume external of said valve assembly.

13. An inflator as set forth in Claim 10 wherein said opening communicates said second volume external of said valve assembly.

14. An inflator as set forth in Claim 10 wherein said electrical signal responsive device is a squib.

15. An inflator as set forth in Claim 1 further comprising a first spring in said first volume engagingly disposed between said assembly and said moveable member and a second spring in said second volume engagingly disposed between said assembly and said moveable member, each of said first spring and said second spring having a respective spring constant selected to determine the initial position of said moveable member.

16. An inflator as set forth in Claim 15 wherein each of said first spring and said second spring respectively have a temperature expansion coefficient selected to determine a temperature dependent initial position of said moveable member.

17. An inflator as set forth in Claim 1 wherein said valve further includes a first pilot orifice disposed within a selected one of said housing and said moveable member, said pilot orifice being interposed said flow path and said second volume to communicate said gas from said second volume to said flow path such that pressure decreases in said second volume to move said moveable member in a direction toward said second volume, the diameter of said pilot orifice being selected to control the rate of displacement of said moveable member.

18. An inflator as set forth in Claim 17 wherein said source includes a vessel having a reservoir chamber and further wherein said valve further includes a second pilot orifice interposed said first volume and said reservoir chamber to communicate said pressurized gas from said reservoir chamber to said first volume when said outlet opening is closed, said second pilot orifice having a diameter substantially less than a diameter of said first pilot orifice.

19. An inflator as set forth in Claim 18 wherein said second pilot orifice is disposed in said housing.

20. An inflator as set forth in Claim 19 wherein said first pilot orifice is disposed in said moveable member.

21. An inflator as set forth in Claim 1 wherein said valve further includes a spring disposed in said second volume interposed said housing and said moveable member to bias said moveable member in an initial position toward said first volume.

22. An inflator as set forth in Claim 21 wherein said second end of said moveable member has a bore and said housing has a bore coaxial with and facing said bore of said moveable member, said spring being disposed in each said bore.

23. An inflator as set forth in Claim 1 wherein said internal chamber has an annular lip, said moveable member abutting said lip when in said initial position.

24. An inflator comprising: a vessel having a reservoir chamber to contain an immediately releasable pressurized gas, said vessel having a top portion and a normally closed outlet opening disposed in said top portion; and a valve disposed within said vessel adjacent said top portion, said valve having a housing and a moveable member; said housing having an internal chamber, an inlet orifice and an outlet orifice, each of said inlet orifice and said outlet orifice being in fluid communication with said chamber to define a flow path from said inlet orifice to said outlet orifice through said chamber, said inlet orifice being adapted to receive said gas from said vessel upon release of said gas, said inlet orifice being in fluid communication with said reservoir chamber, said outlet orifice being disposed adjacent said outlet opening; and said moveable member being disposed within said internal chamber and being normally biased in an initial position, said moveable member having a first end, a second end, an outer portion disposed in slideable engagement with said housing and an open portion disposed in said flow path, said moveable member defining a first volume having a first volume pressure in said internal chamber between said housing and said first end and a second volume having a second volume pressure in said internal chamber between said housing and said second end wherein said first volume is in fluid communication with said reservoir chamber and said second volume is in fluid communication with said flow path such that said first pressure and said second pressure are substantially equal when said outlet opening is closed, said outer portion being disposed in a partially restrictive arrangement with a portion of at least one of said inlet orifice and said outlet orifice to determine an initial cross sectional area of said flow path, said moveable member being controllably displaced in response to pressurized gas being released through said outlet opening when said outlet opening is opened to develop a gas flow within said flow path, said second volume pressure decreasing in response to said gas flow which develops a pressure differential between said first volume and said second volume, said moveable member being displaced from said initial position in response to said pressure differential, said portion of said at least one of said inlet orifice and said outlet orifice in said restrictive arrangement with said outer portion being varied upon displacement of said moveable member thereby varying said cross sectional area of said flow path.

25. An inflator as set forth in Claim 24 wherein said valve further includes a first pilot orifice disposed within a selected one of said housing and said moveable member, said pilot orifice being interposed said flow path and said second volume to communicate said gas from said second volume to said flow path such that pressure decreases in said second volume to move said moveable member in a direction toward said second volume, the diameter of said pilot orifice being selected to control the rate of displacement of said moveable member.

26. An inflator as set forth in Claim 25 wherein said valve further includes a second pilot orifice interposed said first volume and said reservoir chamber to communicate said pressurized gas from said reservoir chamber to said first volume when said outlet opening is closed, said second pilot orifice having a diameter substantially less than a diameter of said first pilot orifice.

27. An inflator as set forth in Claim 26 wherein said second pilot orifice is disposed in said housing.

28. An inflator as set forth in Claim 25 wherein said first pilot orifice is disposed in said moveable member.

29. An inflator as set forth in Claim 24 wherein said moveable member is a spool having a generally cylindrical outer portion in axial slideable engagement within said internal chamber and an indented portion within said flow path.

30. An inflator as set forth in Claim 24 wherein said valve further includes a spring disposed in said second volume interposed said housing and said moveable member to bias said moveable member in an initial position toward said first volume.

31. An inflator as set forth in Claim 30 wherein said second end of said moveable member has a bore and said housing has a bore coaxial with and facing said bore of said moveable member, said spring being disposed in each said bore.

32. An inflator as set forth in Claim 24 wherein said internal chamber has an annular lip, said moveable member abutting said lip when in said initial position.