TUBULAR DUAL STAGE INFLATOR

TUBULAR DUAL STAGE INFLATOR

The present invention relates to a gas generator or airbag inflator utilized in a motor vehicle for inflating an airbag.

In an airbag system, there is typically a gas source and an inflatable restraint device, commonly known as an airbag. In a vehicle crash, the gas source is actuated whereby gas is rapidly channeled into a folded airbag. The inflated airbag provides an energy-absorbing cushion that protects a vehicle occupant during a crash.

The airbag needs to be fully deployed before the vehicle occupant interacts with the airbag less than 100 milliseconds after the crash occurs. The rapidly inflating airbag has a deployment force that may be applied to the vehicle occupant if the airbag is not fully deployed before the vehicle occupant interacts with the airbag. Children or small adults may be positioned too close to an airbag module so they may interact with a deploying airbag. An out-of- position adult, such as an adult leaning forward when a crash occurs, may also interact with a deploying airbag.

A dual stage or multiple stage inflator has the flexibility of providing a constant gas flow rate into the airbag similar to a single stage inflator, but the dual stage inflator may also provide varying gas flow rates. A dual stage inflator may have pyrotechnic material, stored gas, or some combination thereof. A pyrotechnic dual stage inflator has two ignition systems and two gas generants. A first ignition system ignites only the first gas generant and a second ignition system ignites only the second gas generant. The dual stage inflator provides a constant gas flow rate by igniting both the first and second gas generants at the same time. Since the dual stage inflator has two ignition systems, the gas generants may be ignited at different times, which varies the gas flow rate. The second gas generant may be ignited while the first gas generant is burning, and the second gas generant may also be ignited after the first gas generant is no longer generating any inflation gas. The dual stage inflator will completely inflate an airbag like the single stage inflator, but has the advantage of having the ability to have a low onset inflation rate. The low onset inflation rate is beneficial where a child or small adult will interact with an airbag while the airbag is being deployed. In these circumstances, the likelihood of the inflating airbag injuring the vehicle occupant is reduced because the inflation rate is lowered. Preferably, after the vehicle occupant interacts with the inflating airbag, the second gas generant is ignited to fill the remainder of the airbag.

There is a need to design cheaper and simpler dual stage inflators.

There is provided in accordance with the present invention an inflator with a tubular configuration with the combustion chambers arranged side-by- side. The inflator has a symmetrical design with two combustion chambers. Each combustion chamber has an igniter assembly, gas generant, and a wire filter. A bulkhead separates the inflator into first and second combustion chambers. The combustion chambers are isolated from one another so that sympathetic ignition does not occur. The gas generant in a given combustion chamber will only ignite if the igniter assembly in the same combustion chamber is fired. Another aspect of the inflator is the use of a single plastic material molded around an igniter core. During a crash the igniter is fired, which ignites the enhancer, which in turn ignites the gas generant to produce inflation gas, which is channeled into an airbag.

FIG. 1 is a perspective view of the inflator in accordance with the present invention.

FIG. 2 is an exploded view of the inflator shown in FIG. 1.

FIG. 3 is a cross section view along the longitudinal axis of the inflator shown in FIG. 1.

FIG. 4 shows an isometric view of an igniter assembly having an enhancer pellet.

The inflator in accordance with the present invention is a tubular inflator with the combustion chambers arranged in a side-by-side configuration. US 6 149 193 teaches a similar designed tubular inflator and is incorporated herein in its entirety. In FIG. 1 an inflator 10 has essentially a tubular shape with a plurality of exit ports around the circumference thereof. The exit ports provide a channel or passageway through the inflator housing 11 for the inflation gas to escape the inflator 10. The inflation gas generated by the inflator 10 is utilized to inflate an airbag (not shown) during a vehicle crash to protect a vehicle occupant. In FIG. 1 , there are two rows of exit ports, a first row of exit ports 12 receive inflation gas from the first combustion chamber 57 and a second row of exit ports 13 receive inflation gas from the second combustion chamber 58. The first row of exit ports 12 and the second row of exit ports 13 are disposed around the circumference of the inflator housing 11 in an arrangement so that the inflator 10 is thrust neutral while inflation gas is exiting the inflator 10. The number and size of the exit ports may be modified without departing from the scope of the present invention.

FIG. 1 shows the first and second end caps 14, 15 of the present invention. The first end cap 14 and second end cap 15 are attached to opposite ends of the housing 11. The end caps 14, 15 are each secured to the housing 11 via a circumferential weld such as a friction weld, tungsten inert gas (TIG), laser, and the like. The end caps 14, 15 are mounted flush with the housing 11 whereby the diameters of the end caps are substantially equal to the diameter of the housing 11. The housing 11 and end caps comprise a metallic material such as aluminum, steel, and the like. The housing 11 and the end caps 14, 15 are non-gas permeable to prevent moisture from entering the inflator 10 and are able withstand elevated combustion pressures during the burning of the gas generant 51.

FIG. 2 shows an exploded view of the inflator 10 showing the various physical components. The inflator 10 in the present invention is symmetrical with regards to the physical components within the combustion chambers. The combustion chambers represented in FIGS. 2 and 3 do not have the same dimension; the embodiment shown in the FIGS has combustion chambers of unequal volume whereby the first combustion chamber 57 has a smaller volume or size than the second combustion chamber 58. The unequal volume chambers allow the inflator gas output to be more easily tailored to the crash situation. An inflator 10 having equal combustion chambers is within the scope of the present invention. The housing 11 has a bulkhead 55 that divides the interior volume of the housing 11 into two portions, the first combustion chamber 57 and the second combustion chamber 58. The housing 11 comprises aluminum, low carbon steel, or any other metal/alloy that is not gas permeable and that does not fragment during the burning of the gas generant 51. The preferred method of manufacturing the housing 11 with the bulkhead 55 is by a double punching operation, whereby two punches force metal from both ends of the housing 11. Thus, the bulkhead 55 comprises the same material as the remainder of the housing 11. The bulkhead 55 separates the first combustion chamber 57 from the second combustion chamber 58. The bulkhead 55 along with the filters 45, 48 prevent sympathetic ignition, which is defined herein as the ignition of a gas generant in one combustion chamber by the burning of the gas generant in the other combustion chamber. Sympathetic ignition would occur for example when the gas generant 51 is deliberately ignited in the first combustion chamber 57 by the first igniter, and the heat and energy associated with the burning of the gas generant 51 ignite the gas generant 51 in the second combustion chamber 58. The bulkhead 55 and the filter absorb the heat from the burning of the gas generant 51 to prevent sympathetic ignition.

In FIG. the first combustion chamber 57 has a smaller volume than the second combustion chamber 58, however the volume from the first combustion chamber 57 may be equal or greater than the volume of the second combustion chamber 58. The first filter 45 is disposed adjacent to the bulkhead 55 whereby the exit ports 12 for the first combustion chamber 57 are aligned with the first filter 45. In other words, the first filter 45 is arranged with the first combustion chamber 57 so that the entire opening for each exit port is within the geometric planes formed on the top 46 and bottom 47 of the first filter 45. This arrangement of the first filter 45 helps to ensure that inflation gas passes through the filter before exiting the inflator 10 via the exit ports 12. The second row of exit ports 13 is aligned with the second filter 48.

The inflator 10 has first and second row of exit ports 12, 13. The first row of exit ports 12 provide a passageway for the inflation gas to travel out of the first combustion chamber 57 and the second row of exit ports 13 provide a passageway for the inflation gas to flow out of the second chamber 58. Even though the FIGS show only one row of exit ports for each combustion chamber, there may be more than one row of exit ports for each combustion chamber as long as all the exit ports are aligned with the filters 45, 48. This alignment ensures that the inflation gas must pass through the filter before exiting the inflator 10. A row of exit ports as used herein refers to exit ports arranged around the circumference of the housing 11 whereby all of the exit ports in the row are positioned the same distance from the end of the housing 11. The distance is measured from the center of the exit ports along a path parallel with the longitudinal axis of the housing 11 to the end of the housing 11. The exit ports are preferably covered with a foil 56 such as aluminum or stainless steel foil to prevent the incursion of water vapor. The foil 56, sometimes referred to as "burst foil" is typically of a thickness of from 0.01 to about 0.20 mm. The foil 56 is typically adhered to the interior surface of the housing 11 through the use of an adhesive.

The filters 45, 48 comprise compressed knitted metal wire. The metal wire traps solid particles or slag to prevent these particles from exiting the inflator 10 and entering the airbag. The combustion of gas generants does not yield one hundred percent gas, and thus the filter prevents these solid combustion products from exiting the inflator 10. The filter also acts as a heat sink to reduce the temperature of the hot inflation gas. The first filter 45 has a width that is less than half the length for the housing surrounding the first combustion chamber 57. The width of the filter is defined herein as the dimension of the filter between the top 46 and bottom 47 of the filter. The width of the second filter is less than half the length of the housing surrounding the second combustion chamber 58. Each filter is disposed in the inflator 10 so that the filter contacts the bulkhead 55 or that there is an insubstantial gap between the filter and the bulkhead 55. Each filter may also contact the interior surface of the housing 11. As used herein the interior surface of the housing 11 includes the interior portion of the cylindrical portion of the housing 11 and does not include any portion of the bulkhead 55. It is desirable for a gap 59 or plenum to exist between the interior surface of the housing 11 and each filter. The gap 59 may be maintained by a position ring or self-centering filter.

A first position ring 40 is situated in the first combustion chamber 57 and the second position ring 41 is situated in the second combustion chamber 58. Each position ring is a circular metal member held in position within the inflator 10 by an interference fit with the housing 11. Each position ring has a circular ledge 42 for receiving a portion of filter situated in the same combustion chamber. Alternatively, the gap 59 around each filter may be maintained by incorporating ridges or protrusions in the filters (not shown). The integrally formed ridges would contact the housing 11 while keeping the rest of the filter away from the housing 11. The purpose of the gap 59 is to reduce the probability of the filter clogging the exit ports during the burning of the gas generant 51. The burning of the gas generant 51 produces a significant amount of heat that could melt a portion of the filter. The gap 59 minimizes the chance of the melted filter clogging the exit ports and allows for better use of the filter. The gap 59 allows gas to penetrate and pass through the filter without localizing the exiting of the hot gasses and better utilizing the entire filter.

FIG. 3 shows the location of the gas generant 51 inside the inflator 10. The gas generant 51 is a mixture of a fuel and oxidizer that rapidly burn upon ignition. The gas generant 51 provides inflation gas for inflating an airbag. The inflator 10 will function properly with a variety of fuels and oxidizers. Some examples of fuels for the gas generator include high nitrogen content organic compound and the metal salts thereof. Some examples of oxidizers are: metal nitrate, metal oxide, metal chlorate, metal perchlorate, and ammonium nitrate. The gas generant 51 is pressed into tablets and the tablets are randomly placed into the combustion chambers. The gas generant 51 may occupy space in the middle of the filters 45, 48.

The inflator 10 includes first and second igniter assemblies for igniting the gas generant 51. Each igniter assembly 25, 26 is secured to an end cap 14, 15 by threads. Other attachment means are within the scope of the present invention including crimping, welding, and the like. Each igniter assembly 25, 26 has the same physical components as the other. The discussion of the physical components of the igniter assembly applies to both the first and second igniter assemblies 25, 26. The igniter assembly has an igniter core 30, a plastic overmold, and enhancer tablet 50, as shown in FIG. 4. The igniter core 30 or squib utilized in the first igniter assembly 25 is an electrically actuated igniter. The electrodes 31 on the igniter core 30 are isolated from one another and connecting to one another via a bridge wire or surface mounted bridge. The bridge wire is preferably embedded in one or more layers of ignition material and is designed to generate sufficient heat and energy to ignite the enhancer tablet 50. Igniter core suppliers include SDI and EMS-Patvag. Preferably the igniter core 30 is a bridge wire igniter, but a semiconductor bridge igniter or smart igniter may also be employed.

The igniter core 30 is surrounded by a single plastic overmold 32. The plastic overmold 32 comprises a single plastic material and is placed around the igniter core 30 by injection molding or any suitable process that creates a mold around the igniter core 30. The thermoplastic material must not melt below 200° C to resist melting during the combustion of the gas generant 51. The plastic overmold 32 should be shock resistant and good moisture barrier. Suitable thermoplastic materials include nylon 6, nylon 66, ultem, and the like.

The plastic overmold 32 provides threads 33 for fastening the igniter assembly to the end cap. The plastic overmold 32 provides a retainer portion 35 for retaining an enhancer tablet 50. The end cap 14, 15 has an opening 16 therethrough for receiving the igniter assembly 25, 26 having threads 33. The igniter assembly is twisted or screwed into the end cap and this fastening means provides a hermetic seal. In FIG. 3, after the igniter assembly 25, 26 is attached to the end cap 14,15, the electrodes 31 of the igniter core extend to the end of the end cap, but do not extend beyond the end of the end cap. In FIG. 4, the plastic overmold 32 also provides a retainer portion 35 having slots parallel with the longitudinal axis of the igniter assembly creasing a plurality of concave walls 36. The concave walls 36 define a cavity 34 for receiving the enhancer tablet 50. Each of the concave walls 36 flexes outward and this flexing movement allows the enhancer tablet 50 to slide into the cavity 34. After the enhancer tablet 50 is disposed in the cavity 34, the concave walls 36 flex back to the original position thereby securing the enhancer tablet 50 in place. The flexing retainer portion 35 allows the enhancer tablet to be snapped on to the face of the igniter eliminating the need for an enhancer tube or confinement tube.

One or more enhancer tablets may be inserted into the igniter assembly. The enhancer tablet 50 is a gas generating material comprising a fuel and an oxidizer that rapidly burns upon ignition. The enhancer tablet 50 may comprise any of the fuels and oxidizers identified above during the discussion of the gas generant 51 for the present invention. The enhancer tablet 50 needs to be easily ignited and burn at hot temperatures to quickly ignite the gas generant 51. Even though the enhancer generates inflation gas that contributes to the overall gas output of the inflator 10, the primary purpose of the enhancer is to rapidly ignite the gas generant 51.

The inflator 10 operates by the receipt of an electrical signal by the first and/or second igniter assemblies. The electrical signal triggers the ignition of the ignition train resulting in the filling of the airbag. The electrical signal passes through the bridge wire, which produces heat to ignite the ignition material, which in turn ignites the enhancer, which in turn ignites the gas generant 51. The inflation gas produced by burning the gas generant 51 inflates the airbag. Due to the two independent combustion chambers in the inflator 10, the inflator can be tuned to release the optimal amount of inflation gas in a crash. Several contemplated deployment scenarios include the firing of only one igniter assembly, the firing of the igniter assemblies at different times, and the firing of the igniter assemblies simultaneously. The design of the inflator 10 does not permit sympathetic ignition. The gas generant 51 in the first combustion chamber 57 will only ignite if the first igniter assembly 25 is fired. The gas generant 51 in the second combustion chamber 58 will only ignite if the second igniter assembly 26 is fired.