Patent Application
20070001437
The present invention relates to airbag inflators, more specifically a single stage driver side inflator.
The deployment of an airbag module requires a device for rapid, controlled release of a gaseous fluid. This device is commonly referred to as an inflator.
The inflator uses a gas generant that when ignited rapidly generates a large but controlled release of hot gases to fill the airbag.
As shown in
More commonly used, but quite a bit more complex is a dual stage inflator. The dual stage inflators require two initiators and separate enhancer and gas generant chambers. The squibs can be fired one first then the second after a delay or may only fire one squib not firing the second squib at all or both squibs can be fired simultaneously. One such device can be found in U.S. Pat. No. 6,648,370 B1.
Dual stage inflators are obviously more complex and costlier than a single stage inflator. The dual stage inflator also requires typically more enhancer charge to permit the deployment sequence to perform adequately in a sequential fashion with sufficient dwell time during deployment. Single stage inflators are far simpler in design based on fewer components and a simpler firing initiation. Dual stage inflators offer a variable range of protection to passengers, which a single stage inflator cannot provide. Therefore, the use of single stage inflators is far from simple in design complexity when factored into the various requirements of passenger protection. For this reason the use of single stage inflators has been decreasing in spite of the benefits of cost, reliability and simplicity.
In a related, but somewhat ignored consideration is the fact that assembly lines building dual stage inflators are not readily compatible with automated tooling and fixtures used in building single stage inflators. As a result a large investment in capital must be laid out for two separate building lines, one for a single stage inflator and a separate line for a dual stage inflator.
The present invention described hereafter provides a single stage inflator with one initiator having a single initiating squib located in an initiator housing, the initiator housing being offset relative to the centerline of the disk shaped inflator housing.
The design can be made compatible with an automated dual stage inflator building line, greatly reducing the required capital cost needed for a second redundant assembly line.
With reference to
On the top portion 104 of the housing 101 is shown a plurality of gas vent holes 108 covered or sealed by a foil type burst tape. A cylindrically shaped annular filter 110 of wire mesh or similar material is shown extending from the top portion 104 to the bottom portion 102. The filter 110 blocks burning particles from passing through the vent opening 108 when the inflator gas generant is ignited. A seal 124 is positioned internal to the annular filter 110 upon which gas generant pellets 120 are located along with auto ignition pellet 122. In a central location of the bottom half portion 102 is an initiator housing assembly 140. The initiator housing assembly 140 has a single initiating squib 142 with projecting electrical connectors 143, 144 adapted to connect to a wiring connector (not illustrated). The initiating squib 142 has an explosive charge encapsulated in one end surrounded by an enhancer charge 150 comprising small pellets 152. When activated the initiating squib 142 ignites causing the enhancer charge 150 to ignite which in turn causes a pressure rise internal to the initiator housing 141 forcing hot particles and expanding gases through small openings 164 thereby igniting the generant pellets 120 and auto ignition pellet 122. This creates a further rise in pressure causing the foil 109 to burst and gases to fill the airbag (not shown) upon deployment. The initiator housing 141 has an opening 162 sealed by an end plate 160. Although the auto ignition pellet is not needed for a normal deployment, it is consumed during deployment. In the event that the inflator is heated by an outside source, the auto ignition pellet will begin to burn at a predetermined level, causing the inflator to deploy without structural failure.
With reference to
On the top portion 14 of the housing 11 is shown a plurality of gas vent holes 18 covered or sealed by a foil type burst tape 19. A cylindrically shaped annular filter 21 of wire mesh or similar material is shown extending from the top portion 14 to the bottom portion 12. The filter 21 blocks burning particles from passing through the vent opening 18 when the inflator gas generant is ignited. A seal 24 is positioned internal to the annular filter 21 upon which gas generant pellets 20 are located along with auto ignition pellet 22. In an offset location of the bottom half portion 12 is an initiator housing assembly 40. The initiator housing assembly 40 has an initiator housing 41 with a single initiator squib 42 with projecting electrical connectors 43, 44 adapted to connect to a wiring connector (not illustrated). The initiator squib 42 has an explosive charge encapsulated in one end surrounded by an enhancer charge 50 comprising small pellets. When activated the initiator squib 42 ignites causing the enhancer charge 50 inside the initiator housing 41 to ignite which in turn causes a pressure rise internal to the initiator housing 41 forcing hot particles and expanding gases through the small openings 64 in the initiator housing 41 thereby igniting the generant pellets 20 and auto ignition pellet 22. This creates a further rise in pressure causing the foil 19 to burst and gases to fill the airbag (not shown) upon deployment in a single stage fashion. The housing 41 has an end opening 62 sealed by an end plate 60. Although the auto ignition pellet is not needed for a normal deployment, it is consumed during deployment. In the event that the inflator is heated by an outside source, the auto ignition pellet will begin to burn at a predetermined level, causing the inflator to deploy without structural failure.
Referring to
It is desirable to pelletize the gas generant composition. To do so, up to about 5.0 weight %, typically 0.2-5 weight % of a pressing aid or binder may be employed. These may be selected from materials known to be useful for this purpose and include molybdenum disulfide, graphite, elastomers, polyesters, boron nitride, silicon dioxide, talc, calcium stearate and clays.
The gas generant composition may optionally contain a catalyst at up to about 3 weight %, typically between about 1 and about 2 weight %. Cupric oxide is a representative combustion catalyst.
The initiator housing 41 has the plurality of vent holes or openings 64 oriented to direct exhaust into the gas generant pellets 20 with a strong but directional thrust. The openings 64 are located less than 270 degrees, preferably less than 180 degrees around the periphery of the initiator housing 41 in the direction of the gas generant pellets 20 as shown. To compensate for this strong directional thrust effect, the holes 18 on the inflator housing top portion 14 are radially oriented about 360° in a spaced pattern and as these gases move radially outwardly the overall thrust becomes almost thrust neutral with an almost immeasurable thrust bias opposite the initiator housing 41.
With reference to
In testing of the inventive inflator 10, it was determined that the enhancer charge should be increased to about 2.0 grams, and the initiating squib charge to be in the range of 180 to 260 mg of zirconium potassium perchlorate (ZPP) for proper performance in terms of airbag deployment. Initiator booster charges in excess of 260 mg were not necessary and in fact could potentially damage the initiator housing by exceeding rated burst pressures of the crimp. Lower amounts of charge, below 180 mg, could cause a delay in the gas generant burning and lead to unsatisfactory airbag deployment pressure or fill rates.
Empirical studies show that the size of the pellets of the enhancer could be beneficially altered to increase or improve surface area for rapid burn rates, accordingly, a pellet having a 4 mm diameter and a 1.2 mm length was found to be ideal from a pressure versus time analysis.
In
In
As a result of these empirical charts it was projected that a more preferred gas generant pellet 20 size for the offset inflator 10 was a size of 8.0 mm diameter by 2.0 mm length.
For comparison purposes, the dual stage inflator with two initiators uses 180 mg of initiator booster charge and the enhancer charge is 1.1 grams in the primary initiator housing and 1.3 grams in the secondary initiator housing. The present invention uses 180 to 260 mg of initiator booster charge and 2.0 grams of enhancer. This represents a 0.4 gram reduction in the enhancer. The enhancer pellets 50 are more expensive and burn with more toxicity than the generant pellets 20, accordingly, the reduction in enhancer load is believed to be a valuable improvement.
Another benefit of the single stage offset design is it has 20% more free volume than the dual stage inflator. This means the height of the inflator housing could be reduced by at least 10% if further miniaturization is desirable.
The current invention uses an internal spacer of aluminum to occupy the free volume space and thus the housing upper and lower portions are almost identical to the dual stage housing permitting either style to be used on the same production line.
Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which would be within the full intended scope of the invention as defined by the following appended claims.
