Autoignition of a fluid fueled inflator

What is claimed is:

1. An apparatus for inflating an inflatable device, said apparatus comprising:

a fluid fuel storage element storing at least one fuel in the form of a fluid and free of combustion oxidant,

a first chamber in fluid communication with said fluid fuel storage element upon opening of said fluid fuel storage element, said first chamber including at least one gas exit opening and having sealing means normally closing said gas exit opening, and wherein, in normal operation, the at least one fuel and at least one stored oxidant are burned to produce combustion products including hot combustion gas, with the combustion of the at least one fuel and the at least one stored oxidant increasing the temperature and pressure within said first chamber, said first chamber sealing means adapted to open when a predetermined increase in pressure within said first chamber is realized,

whereby, in normal operation, at least a portion of said hot combustion gas is expelled from said first chamber,

a second chamber containing a supply of pressurized stored gas, said second chamber in fluid communication with said first chamber upon the opening of said first chamber sealing means, with said second chamber including at least one gas exit port and having sealing means normally closing said gas exit port, in normal operation said hot combustion gas expelled from said first chamber mixing with said pressurized stored gas to produce inflation gas, the mixing of said hot combustion gas with said pressurized stored gas increasing the temperature and pressure within said second chamber, said second chamber sealing means adapted to open when a predetermined increase in pressure within said second chamber is realized after said hot combustion gas expelled from said first chamber mixes with said pressurized stored gas to produce said inflation gas,

whereby, in normal operation, at least a portion of said inflation gas is expelled from said second chamber to inflate said device, and

initiator means for initiating the burning of the at least one fuel and the at least one oxidant in normal operation,

wherein under autoignition operation, at a predetermined first temperature greater than the ambient temperature range to which said inflation apparatus is normally subjected, said fluid fuel storage element opens and at least a portion of the at least one fuel contacts an oxidant in said first chamber, with the at least one fuel being characterized in igniting when exposed to the oxidant at a predetermined second temperature, greater than the ambient temperature range to which said inflation apparatus is normally subjected.

2. The apparatus of claim 1 wherein the fuel in the form of a fluid includes a liquid form.

3. The apparatus of claim 1 wherein the fuel in the form of a fluid comprises a multi-phase combination of liquid and finely divided solid.

4. The apparatus of claim 1 wherein the fuel in the form of a fluid is a hydrocarbon-based fuel.

5. The apparatus of claim 1 wherein the fuel in the form of a fluid includes ethyl alcohol.

6. The apparatus of claim 1 wherein the fuel in the form of a fluid includes propyl alcohol.

7. The apparatus of claim 1 wherein the fuel in the form of a fluid includes at least one C.sub.2 -C.sub.4 alkane.

8. The apparatus of claim 1 wherein, under autoignition operation, the oxidant with which the at least one fuel is burned comprises the at least one stored oxidant.

9. The apparatus of claim 1 where in, under autoignition operation, the oxidant with which the at least one fuel is burned comprises air.

10. The apparatus of claim 1 wherein said fluid fuel storage element stores a mixture comprising a primary fuel and an autoignition enhancing material.

11. The apparatus of claim 10 wherein the autoignition enhancing material is a paraffinic fuel selected from the group consisting of n-octane, n-heptane and n-hexane.

12. The apparatus of claim 10 wherein the autoignition enhancing material is a petroleum distillates selected from the group consisting of diesel fuel, JP-4, and gasoline.

13. The apparatus of claim 10 wherein the autoignition enhancing material is a mineral oil.

14. The apparatus of claim 1 wherein the predetermined second temperature is at least as great as the predetermined first temperature.

15. The apparatus of claim 1 wherein the predetermined first temperature and the predetermined second temperature are substantially the same.

16. The apparatus of claim 1 wherein the predetermined first temperature is greater than the predetermined second temperature.

17. The apparatus of claim 1 wherein the predetermined first temperature is less than the predetermined second temperature.

18. An apparatus for inflating an inflatable device, said apparatus comprising:

a liquid fuel storage element storing at least one liquid fuel free of combustion oxidant,

a first chamber in fluid communication with said liquid fuel storage element upon opening of said liquid fuel storage element, said first chamber including at least one gas exit opening and having sealing means normally closing said gas exit opening, and wherein, in normal operation, the at least one liquid fuel and at least one stored oxidant are burned to produce combustion products including hot combustion gas, with the combustion of the at least one liquid fuel and the at least one stored oxidant increasing the temperature and pressure within said first chamber, said first chamber sealing means adapted to open when a predetermined increase in pressure within said first chamber is realized,

whereby, in normal operation, at least a portion of said hot combustion gas is expelled from said first chamber,

a second chamber containing a supply of pressurized stored gas, said second chamber in fluid communication with said first chamber upon the opening of said first chamber sealing means, with said second chamber including at least one gas exit port and having sealing means normally closing said gas exit port, in normal operation said hot combustion gas expelled from said first chamber mixing with said pressurized stored gas to produce inflation gas, the mixing of said hot combustion gas with said pressurized stored gas increasing the temperature and pressure within said second chamber, said second chamber sealing means adapted to open when a predetermined increase in pressure within said second chamber is realized after said hot combustion gas expelled from said first chamber mixes with said pressurized stored gas to produce said inflation gas,

whereby, in normal operation, at least a portion of said inflation gas is expelled from said second chamber to inflate said device, and

initiator means for initiating the burning of the at least one liquid fuel and the at least one oxidant in normal operation,

wherein under autoignition operation, at a predetermined first temperature greater than the ambient temperature range to which said inflation apparatus is normally subjected, said liquid fuel storage element opens and at least a portion of the at least one liquid fuel contacts an oxidant in said first chamber, with the at least one liquid fuel being characterized in igniting when exposed to the oxidant at a predetermined second temperature at least as great as the predetermined first temperature.

19. The apparatus of claim 18 wherein, under autoignition operation, the oxidant with which the at least one fluid fuel is burned comprises the at least one stored oxidant.

20. The apparatus of claim 18 wherein, under autoignition operation, the oxidant with which the at least one fluid fuel is burned comprises air.

21. The apparatus of claim 18 wherein said fluid fuel storage element stores a mixture comprising a primary fuel and an autoignition enhancing material.

22. A method for autoignition operation of an apparatus for inflating an inflatable device, wherein the apparatus includes a fluid fuel storage element storing at least one fuel in the form of a fluid and free of combustion oxidant, with the apparatus also including a closed combustion chamber in fluid communication with the fluid fuel storage element upon opening of the fluid fuel storage element, said method comprising the step of:

heating the inflation apparatus whereby at a predetermined first temperature greater than the ambient temperature range to which the inflation apparatus is normally subjected, the fluid fuel storage element opens and at least a portion of the fuel contacts an oxidant in the closed combustion chamber, with the fuel igniting when exposed to the oxidant at a predetermined second temperature, greater than the ambient temperature range to which the inflation apparatus is normally subjected to produce combustion products, with the closed combustion chamber opening when a predetermined increase in pressure within the first chamber is realized.

23. The method of claim 22 wherein the predetermined second temperature is at least as great as the predetermined first temperature.

24. The method of claim 32 wherein the predetermined first temperature and the predetermined second temperature are substantially the same.

25. The method of claim 32 wherein the predetermined first temperature is greater than the predetermined second temperature.

26. The method of claim 22 wherein the predetermined first temperature is less than the predetermined second temperature.

27. A method of autoignition operation of an apparatus for inflating an inflatable device, wherein the apparatus includes a fluid fuel storage element storing at least one fuel in the form of a fluid and free of combustion oxidant, said method comprising the steps of:

heating the inflation apparatus whereby at a predetermined first temperature greater than the ambient temperature range to which the inflation apparatus is normally subjected, the fluid fuel storage element opens and at least a portion of the at least one fuel contacts an oxidant, with the at least one fuel igniting when exposed to the oxidant at a predetermined second temperature, greater than the ambient temperature range to which said inflation apparatus is normally subjected,

burning the at least one fuel with the oxidant in a first sealed chamber to produce combustion products including hot combustion gas, wherein the first sealed chamber includes at least one gas exit opening normally closed by a sealing means, said burning increasing the temperature and pressure within the first chamber,

opening the first chamber sealing means to expel the hot combustion gas from the first chamber into a second chamber containing a supply of pressurized stored gas,

mixing the expelled hot combustion gas with the pressurized stored gas in the second chamber to produce inflation gas, wherein the second chamber includes at least one gas exit port normally closed by a sealing means, said mixing increasing the temperature and pressure within the second chamber, and

opening the second chamber port sealing means to expel the inflation gas from the second chamber to inflate the inflatable safety device.

28. A method of autoignition operation of an apparatus for inflating an inflatable device, wherein the apparatus includes a fluid fuel storage element storing at least one fuel in the form of fluid and free of combustion oxidant, said method comprising the step of:

heating the inflation apparatus whereby at a predetermined first temperature greater than the ambient temperature range to which the inflation apparatus is normally subjected, the fluid fuel storage element opens and at least a portion of the at least one fuel contacts an oxidant, with the at least one fuel igniting when exposed to the oxidant at a predetermined second temperature, greater than the ambient temperature range to which the inflation apparatus is normally subjected, wherein the inflation apparatus also includes:

a first chamber containing a supply of stored oxidant, the first chamber in fluid communication with the fluid fuel storage element upon opening of the fluid fuel storage element, the first chamber including at least one gas exit opening and having sealing means normally closing the gas exit opening, and

a second chamber containing a supply of pressurized stored gas, the second chamber in fluid communication with the first chamber upon the opening of the gas exit opening sealing means, with the second chamber including at least one gas exit port and having sealing means normally closing the gas exit port,

wherein said method, prior to the igniting of the at least one fuel, additionally comprises the steps of:

opening the second chamber sealing means to vent at least a portion of the pressurized stored gas,

followed by, opening the first chamber sealing means to vent at least a portion of the stored oxidant to vent through the open second chamber.

29. A method for autoignition operation of an apparatus for inflating an inflatable device, wherein the apparatus includes a fluid fuel storage element storing at least one fluid fuel in the form of a fluid and free of combustion oxidant, with the apparatus also including a closed combustion chamber in fluid communication with the fluid fuel storage element upon opening of the fluid fuel storage element, said method comprising the steps of:

opening the closed combustion chamber,

followed by opening the fluid fuel storage element when the inflation apparatus is heated to a predetermined first temperature greater than the ambient temperature range to which the inflation apparatus is normally subjected whereby at least a portion of the fuel contacts an oxidant in the combustion chamber, with the fuel igniting when exposed to the oxidant at a predetermined second temperature, greater than the ambient temperature range to which the inflation apparatus is normally subjected.

30. The method of claim 29 wherein the predetermined second temperature is at least as great as the predetermined first temperature.

31. The method of claim 29 wherein the predetermined first temperature and the predetermined second temperature are substantially the same.

32. The method of claim 29 wherein the predetermined first temperature is greater than the predetermined second temperature.

33. The method of claim 29 wherein the predetermined first temperature is less than the predetermined second temperature.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

This invention relates generally to inflatable restraint systems and gas generators used to inflate devices such as a vehicle occupant restraint (commonly known as an air bag). More particularly, the invention relates to the autoignition of such gas generators.

It is well known to protect a vehicle occupant using a cushion or bag that is inflated/expanded with gas, e.g., an "air bag" when the vehicle encounters sudden deceleration, such as in a collision. In such systems, the cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the inflatable restraint system, the air bag is commonly inflated in a matter of a few milliseconds with gas produced by a device commonly referred to as "a gas generator" or "an inflator."

Many types of inflator devices have been disclosed in the art for inflating an air bag for use in an inflatable restraint system. One type of inflator device involves the utilization of a quantity of stored compressed gas which is selectively released to inflate the air bag. To properly inflate a typical air bag at an appropriate rate, such a type of device commonly requires the storage of a relatively large volume of gas at relatively high pressures. As a result of the high pressures, the walls of the gas storage chamber are typically relatively thick for increased strength. The combination of large volume and thick walls results in relatively heavy and bulky inflator designs.

Another type of inflator device derives a gas source from a combustible gas generating material, e.g., a pyrotechnic, commonly ignited by means of an igniter having an ignition agent and which upon ignition generates a quantity of gas sufficient to inflate the air bag. Typically, such gas generating materials can produce various undesirable combustion products, including various solid particulate materials. The removal of such solid particulate material, such as by the incorporation of a filtering device within or about the inflator, undesirably increases inflator design and processing complexity and can increase the costs associated therewith.

In addition, the temperature of the gaseous emission of such inflator devices can typically vary between about 500.degree. F. (260.degree. C.) and 1200.degree. F. (649.degree. C.), dependent upon numerous interrelated factors including the desired level of inflator performance, as well as the type and amount of gas generant material used therein, for example. Consequently, air bags used in conjunction with such inflator devices typically are constructed of or coated with a material resistant to such high temperatures. For example, an air bag such as constructed of nylon fabric, in order to resist burn through as a result of exposure to such high temperatures, can be prepared such that the nylon fabric air bag material is coated with neoprene or one or more neoprene coated nylon patches are placed at the locations of the air bag at which the hot gas initially impinges. As will be appreciated, such specially fabricated or prepared air bags typically are more costly to manufacture and produce.

Further, while vehicular inflatable restraint systems are preferably designed to be properly operational over a broad range of conditions, the performance of such inflator device designs can be particularly sensitive to changes in the ambient conditions, especially temperature. For example, operation at very low temperatures, such as temperatures of -40.degree. F. (-40.degree. C.), can affect the performance of various propellants, and thus reduce the air bag pressure resulting from an inflator which contains a fixed available amount of propellant.

In a third type of inflator device, air bag inflating gas results from a combination of stored compressed gas and combustion of a gas generating material, e.g., a pyrotechnic. This type of inflator device is commonly referred to as an augmented gas or hybrid inflator. Hybrid inflators that have been proposed heretofore are subject to certain disadvantages. For example, inflator devices of such design typically result in a gas having a relatively high particulate content.

Various specific inflator devices and assemblies have been proposed in the prior art. U.S. Pat. No. 5,263,740 discloses an assembly wherein within a single chamber is housed both an inflation gas and a first ignitable material, which is subsequently ignited therein.

The housing of both an inflation gas and an ignitable material within a single chamber can result in production and storage difficulties. For example, concentration gradients of such components, both initially and over time as the device awaits actuation, can increase the potential for the release therefrom of ignitable material into the air bag prior to complete ignition, as well as increasing the relative amount of incomplete products of combustion released into the air bag.

Also, gas generators wherein, for example, a fuel and an oxidant are stored in a single chamber, can under certain extreme circumstances be subject to undesired autoignition (i.e., self-ignition) and the consequent dangers that may be associated therewith, both during manufacture and storage.

Further, as the gas mixture resulting from such a single storage chamber assembly will typically be at a relatively high temperature, such designs can be subject to the same or similar shortcomings identified above associated with high temperature emissions.

In an effort to avoid or minimize at least some of these shortcomings, it has been proposed to store the fuel and oxidant in such single chamber gas generators as a fuel lean mixture. However, operation with fuel lean mixtures can itself be subject to various operational difficulties. For example, such a single chamber gas generator operated with a fuel lean mixture can experience ignition difficulties as it can be difficult to ensure that a fuel lean mixture is completely or sufficiently uniformly combustible so as to not unduly hinder performance.

In addition, as a result of the rapid pressure and temperature rises normally associated with inflator devices which house a mixture of oxidant and ignitable material, proper and desired control and operation of such inflator devices can be difficult and/or complicated.

Inflatable restraint systems have been devised for automotive vehicles in which one or more air bags are stored in one or more storage compartments within the vehicle. In general, an air bag provided for the protection of a vehicle driver, e.g., a driver side air bag, is stored within a housing mounted in a storage compartment located in the steering column of the vehicle. Whereas, an air bag for the protection of a front seat passenger, e.g., a passenger side air bag, is typically stored within a housing mounted in the instrument panel/dash board of the vehicle.

In such systems, the gas generators or inflators must be constructed to withstand large thermal and mechanical stresses during the gas generation process. Thus, gas generators have been fabricated using steel for the casing and other structural components, with the structural components commonly joined together by screw threads, roll crimping or welding.

To satisfy light weight specifications, significant weight reduction can be achieved through the utilization of a light metal or material such as aluminum or an aluminum alloy for the generator housing and other structural components. Gas generators made of such materials typically will not experience problems in ordinary use wherein, during the event of a collision, the ignition agent is ignited, followed by the igniting of the gas generant to generate inflation gas. However, the mechanical strength of such lighter weight materials is lowered when overheated to a high temperature.

For example, a problem is encountered when generators utilizing aluminum for the housing construction are subjected to a high temperature environment, such as a bonfire. This problem stems from the fact that at a temperature in the 650.degree. F. (343.degree. C.) range, the pyrotechnics of the gas generator commonly automatically ignite. In this temperature range, the aluminum of the housing structure degrades and tends to rupture or burst, which in turn can result in the projection of pieces and/or fragments in various directions. This problem is not encountered with gas generators that employ steel in the housing structure since steel does not degrade until a much higher temperature of about 1100.degree. F. (593.degree. C.) is reached. Thus, the use of aluminum, in place of steel, in a gas generator, while serving to reduce the weight of the assembly typically results in the gas generator having a lower internal pressure capability. This lower internal pressure capability could be hazardous in a high temperature environment such as the gas generator might be subjected to in the event of a fire whether in storage, in transit, or after installation in a vehicle.

Moreover, it will be understood that regardless the material of fabrication, gas generators can be prone to rupture under certain specific conditions when subjected to sufficiently aggressive reaction of a gas generant material stored therein.

A previously disclosed solution to this problem is the incorporation of an autoignition device in the gas generator. For example, U.S. Pat. No. 4,561,675, Adams et al., assigned to the assignee of the present invention and which patent is incorporated herein in its entirety, discloses an autoignition device that causes the pyrotechnic material in a gas generator to function when the device is subjected to a predetermined high temperature below the ignition temperature of the solid fuel gas generant. The container of the autoignition device is disclosed as being hat shaped and includes a brim and a crown, with the crown attached in thermal contact with the generator housing and with the area of a wall of the container bound by the brim being closed by a foil seal.

The inclusion of an autoignition material in an inflator housing such as is used for inflators for driver side installations is also disclosed in U.S. Pat. Nos. 5,106,119 and 5,114,179 which disclose a housing apparatus wherein, by means of a piece of aluminum foil, a "packet" of autoignition material is held in place in a recess formed in the canister cover. Also, U.S. Pat. No. 5,186,491 discloses the incorporation of an autoignition material within a recess of the gas generator.

In addition, U.S. Pat. Nos. 4,998,751 and 5,109,772, both assigned to the assignee of the present invention and which patents are incorporated herein in their entirety, generally relate to inflator devices. These patents disclose the incorporation, respectively, of "an autoignition device" and "a container" which "holds or contains autoignition granules" in such gas generators within a centrally located recess. Thus, it is known to place autoignition granules within a container within such an elongated gas generator housing at one end thereof, opposite an end of a elongated igniter tube. Furthermore, it is known to use a cup-shaped container to hold such granules.

Unfortunately, the inclusion of an autoignition material in an inflator can be subject to certain drawbacks including those related to increased expense and reduced dependability. First, an autoignition material added to an inflator assembly must typically be carefully prepared, handled and installed, thereby increasing the expense associated therewith. Also, the aging characteristics of typical autoignition materials, whereby the temperature sensitivity of the material may vary over time and may result in inconsistent performance of an aged autoignition material, thereby reducing the dependability associated therewith.

SUMMARY OF THE INVENTION

A general object of the invention is to provide an improved apparatus and method for inflating an inflatable device such as an inflatable restraint for occupants of motor vehicles.

A more specific objective of the invention is to overcome one or more of the problems described above.

The general object of the invention can be attained, at least in part, through an inflatable device inflation apparatus which includes first and second chambers and initiator means for initiating the burning of at least one fluid fuel and at least one oxidant in the first chamber to produce combustion products including hot combustion gas. The first chamber includes at least one gas exit opening and has sealing means normally closing the gas exit opening. The combustion of the fluid fuel and the oxidant increases the temperature and pressure within the first chamber.

Included are opening means to open the first chamber sealing means whereby at least a portion of the hot combustion gas is expelled from the first chamber. Upon the opening of the gas exit opening sealing means, the second chamber, which chamber contains a supply of pressurized stored gas, is in fluid communication with the first chamber, with the hot combustion gas expelled from the first chamber mixing with the pressurized stored gas to produce inflation gas.

The second chamber includes at least one gas exit port and has sealing means normally closing the gas exit port. The mixing of the hot combustion gas with the pressurized stored gas increases the temperature and pressure within the second chamber.

Also included are opening means to open the second chamber sealing means whereby at least a portion of the inflation gas is expelled from the second chamber to inflate the device.

The prior art fails to provide air bag inflation gas at a sufficiently low temperature and having a sufficiently low concentration of undesirable products of combustion, e.g., incomplete products of combustion and/or particulate matter. In addition, safety and handling concerns such as those associated with the single chamber storage of an inflation gas/ignitable material mixture are not completely satisfied by prior art devices. Further, prior art devices are typically operational only with a relatively narrow variety of fuels and oxidants. In addition, such single chamber devices may produce an undesirably rapid pressure rise. Further, in order to minimize the adverse effects discussed above, proper operation of such prior art devices is typically assured over only limited relative amounts of such fuels and oxidants.

The invention further comprehends an inflatable device inflation apparatus which includes a fluid fuel storage element storing at least one fluid fuel free of oxidant, first and second chambers, and initiator means for initiating the burning of the fluid fuel and at least one oxidant in the first chamber to produce combustion products including hot combustion gas.

The first chamber includes at least one gas exit opening and has sealing means normally closing the gas exit opening. The combustion of the fluid fuel and the oxidant increases the temperature and pressure within the first chamber.

Included are opening means to open the first chamber sealing means whereby at least a portion of the hot combustion gas is expelled from the first chamber. Upon the opening of the gas exit opening sealing means, the second chamber, which chamber contains a supply of pressurized stored gas, is in fluid communication with the first chamber, with the hot combustion gas expelled from the first chamber mixing with the pressurized stored gas to produce inflation gas.

The second chamber includes at least one gas exit port and has sealing means normally closing the gas exit port. The mixing of the hot combustion gas with the pressurized stored gas increases the temperature and pressure within the second chamber.

Also included are opening means to open the second chamber sealing means whereby at least a portion of the inflation gas is expelled from the second chamber to inflate the device.

The invention still further comprehends a method for inflating an inflatable safety device in a vehicle. The method involves the step of burning at least one fluid fuel with at least one oxidant in a first sealed chamber to produce combustion products including hot combustion gas. The first sealed chamber includes at least one gas exit opening normally closed by a sealing means, and the burning increases the temperature and pressure within the chamber. Th